Date | Country | Change |
| 1991 |  Egypt,  South Sudan,  Sudan | Patriarchal Vicariate of Egypt and Sudan (Greek-Melkite Rite) was promoted as Patriarchal Exarchate of Egypt and Sudan |
| 1991 |  Iraq | Patriarchal Exarchate of Basra and the Gulf (Syriac Rite) was established |
| 1991 |  Israel,  Palestine | Patriarchal Exarchate of Jerusalem (Maronite Rite) was established |
| 1991 |  Italy | Titular Episcopal See of Acquapendente was restored |
| 1991 | Italy | Titular Episcopal See of Bagnoregio was restored |
| 1991 | Italy | Titular Episcopal See of Gallese was restored |
| 1991 | Italy | Titular Episcopal See of Nepi was restored |
| 1991 | Italy | Titular Episcopal See of Orte was restored |
| 1991 | Italy | Titular Episcopal See of Sutri was restored |
| 1991 | Italy | Titular Episcopal See of Tuscania was restored |
| 1991 |  Lebanon | Patriarchal Exarchate of Lebanon (Syriac Rite) was established |
| 1991 | Palestine, Israel | Patriarchal Vicariate of Jerusalem (Chaldean Rite) was promoted as Patriarchal Exarchate of Jerusalem |
| 1991 | Palestine | Patriarchal Vicariate of Jerusalem (Greek-Melkite Rite) was promoted as Patriarchal Exarchate of Jerusalem |
| 1991 | Palestine, Israel,  Jordan | Patriarchal Exarchate of Jerusalem (Palestine and Jordan) (Syriac Rite) was established |
| 1991 |  Philippines | Diocese of Gumaca lost territory to Diocese of Daet |
| 1991 |  Poland | Apostolic Administration of Lubaczów was established (from Metropolitan Archdiocese of Lviv) |
| 1991 |  Turkiye | Patriarchal Exarchate of Turkiye (Syriac Rite) was established |
| 1991.01.16 |  Moldova,  Russia | Diocese of Tiraspol lost territory to Diocese of Kamyanets-Podilskyi |
| 1991.01.16 | Poland | Ordinariate of Poland (for Greek and Armenian Catholics) (Eastern Rite) was renamed as Ordinariate of Ordynariat dla wiernych obrządku wschodniego w Polsce |
| 1991.01.16 | Poland | Apostolic Exarchate of Łemkowszczyzna (Ukrainian Rite) was suppressed (to Diocese of Przemyśl) |
| 1991.01.21 | Poland | Military Ordinariate of Ordynariat Polowy Wojska Polskiego was restored |
| 1991.01.31 |  Haiti | Diocese of Fort-Liberté was established (from Metropolitan Archdiocese of Cap-Haïtien and Diocese of Hinche and became suffragan of Cap-Haïtien) |
| 1991.02.16 | Italy | Titular Episcopal See of Montefiascone was restored |
| 1991.02.16 | Italy | Diocese of Viterbo, Acquapendente, Bagnoregio, Montefiascone, Tuscania e San Martino al Monte Cimino was renamed as Diocese of Viterbo |
| 1991.02.22 |  Ecuador | Apostolic Vicariate of Zamora was renamed as Apostolic Vicariate of Zamora |
| 1991.03.17 |  Nigeria | Mission sui juris of Bomadi was established (from Diocese of Port Harcourt and Diocese of Warri) |
| 1991.03.22 | Nigeria | Mission sui juris of Kano was established (from Metropolitan Archdiocese of Kaduna) |
| 1991.03.25 | Italy | Diocese of Albano exchanged territory with Diocese of Latina–Terracina–Sezze–Priverno |
| 1991.03.25 | Italy | Diocese of Latina–Terracina–Sezze–Priverno exchanged territory with Diocese of Albano |
| 1991.04.04 |  Chile | Diocese of Melipilla was established (from Metropolitan Archdiocese of Santiago and became suffragan of Santiago) |
| 1991.04.13 |  Belarus | Diocese of Grodno was established (from Metropolitan Archdiocese of Vilnius, Diocese of Łomża and Diocese of Pinsk and became suffragan of Minsk–Mohilev) |
| 1991.04.13 | Belarus | Diocese of Minsk was promoted as Metropolitan Archdiocese of Minsk–Mohilev (with suffragan sees Grodno, Pinsk and Tiraspol, gained territory from the suppressed Metropolitan Archdiocese of Mohilev and Apostolic Administration of Leningrad and exchanged territory with Diocese of Pinsk) |
| 1991.04.13 | Belarus | Metropolitan Archdiocese of Mohilev was suppressed (to Metropolitan Archdiocese of Minsk–Mohilev, Diocese of Pinsk and Diocese of Žytomyr and to establish Apostolic Administration of European Russia and Apostolic Administration of Novosibirsk) |
| 1991.04.13 | Belarus | Diocese of Pinsk exchanged territory with Diocese of Minsk |
| 1991.04.13 |  Kazakhstan | Apostolic Administration of Kazakhstan was established (from Diocese of Vladivostok and from the suppressed Apostolic Administration of Leningrad) |
| 1991.04.13 | Russia | Apostolic Administration of European Russia was established (from Diocese of Tiraspol and from the suppressed Metropolitan Archdiocese of Mohilev) |
| 1991.04.13 | Russia | Apostolic Administration of Leningrad was suppressed (to Metropolitan Archdiocese of Minsk–Mohilev and to establish Apostolic Administration of Kazakhstan and Apostolic Administration of Novosibirsk) |
| 1991.04.13 | Russia | Apostolic Administration of Novosibirsk was established (from Diocese of Vladivostok and from the suppressed Metropolitan Archdiocese of Mohilev and Apostolic Administration of Leningrad) |
| 1991.04.15 |  Jamaica | Apostolic Vicariate of Mandeville was established (from Metropolitan Archdiocese of Kingston in Jamaica and Diocese of Montego Bay) |
| 1991.04.26 |  Zambia | Diocese of Mbala was renamed as Diocese of Mbala–Mpika |
| 1991.04.30 |  Nicaragua | Territorial Prelature of Jinotega was promoted as Diocese of Jinotega |
| 1991.04.30 | Nicaragua | Territorial Prelature of Juigalpa was promoted as Diocese of Juigalpa |
| 1991.05.20 |  Cameroon | Diocese of Ebolowa–Kribi was established (from Metropolitan Archdiocese of Douala and Diocese of Sangmélima and became suffragan of Yaoundé) |
| 1991.05.20 | Cameroon | Diocese of Yokadouma was established (from Diocese of Bertoua and became suffragan of Yaoundé) |
| 1991.05.20 |  Uganda | Diocese of Kotido was established (from Diocese of Moroto and became suffragan of Kampala) |
| 1991.06.05 | Poland | Diocese of Białystok was established (from Metropolitan Archdiocese of Vilnius and became suffragan of Vilnius) |
| 1991.06.05 | Poland | Diocese of Drohiczyn was established (from Diocese of Pinsk and became suffragan of Vilnius) |
| 1991.06.17 |  Zimbabwe | Diocese of Gokwe was established (from Diocese of Hwange and became suffragan of Harare) |
| 1991.07.05 |  Brazil | Diocese of Cândido Mendes was renamed as Diocese of Zé Doca |
| 1991.07.13 |  Armenia, Belarus,  Estonia,  Georgia,  Latvia,  Lithuania, Russia | Ordinariate of East Europe (Armenian Rite) was established |
| 1991.07.17 | Brazil | Diocese of Cachoeira do Sul was established (from Diocese of Santa Maria and became suffragan of Porto Alegre) |
| 1991.07.23 |  Spain | Diocese of Alcalá de Henares was restored (from Archdiocese of Madrid and became suffragan of Madrid) |
| 1991.07.23 | Spain | Diocese of Getafe was established (from Archdiocese of Madrid and became suffragan of Madrid) |
| 1991.07.23 | Spain | Archdiocese of Madrid was promoted as Metropolitan Archdiocese of Madrid (with suffragan sees Alcalá de Henares and Getafe and lost territory to establish Diocese of Alcalá de Henares and Diocese of Getafe) |
| 1991.08.05 |  Romania | Diocese of Alba Iulia was promoted as Archdiocese of Alba Iulia (without ecclesiastical province) |
| 1991.08.14 | Brazil | Territorial Prelature of Alto Solimões was promoted as Diocese of Alto Solimões (became suffragan of Manaus) |
| 1991.10.01 | Jordan, Israel, Palestine | Patriarchal Exarchate of Jerusalem (Armenian Rite) was established |
| 1991.10.08 |  Myanmar | Diocese of Bassein was renamed as Diocese of Pathein |
| 1991.10.08 | Myanmar | Diocese of Prome was renamed as Diocese of Pyay |
| 1991.10.08 | Myanmar | Metropolitan Archdiocese of Rangoon was renamed as Metropolitan Archdiocese of Yangon |
| 1991.10.11 |  Mozambique | Diocese of Nacala was established (from Metropolitan Archdiocese of Nampula and became suffragan of Nampula) |
| 1991.12.21 |  Ethiopia | Apostolic Prefecture of Meki was promoted as Apostolic Vicariate of Meki |
| 1991.12.24 | Lithuania | Territorial Prelature of Klaipėda was suppressed (to Diocese of Telšiai and united to Diocese of Telšiai) |
