 | 1977 | 1978 | 1979 |  |
Date | Country | Change |
| 1978 |  Italy | Diocese of Ascoli Satriano exchanged territory with Diocese of Bovino |
| 1978 | Italy | Diocese of Bovino exchanged territory with Diocese of Ascoli Satriano |
| 1978 | Italy | Archdiocese of Cosenza lost territory to Diocese of Lungro |
| 1978 |  Slovakia | Apostolic Administration of Szatmár na Slovensku was suppressed (to Diocese of Satu Mare) |
| 1978.01.03 |  Brazil | Territorial Prelature of Coxim was established (from Diocese of Campo Grande and became suffragan of Cuiabá) |
| 1978.01.03 | Brazil | Diocese of Três Lagoas was established (from Diocese of Campo Grande and became suffragan of Cuiabá) |
| 1978.01.03 | Brazil | Territorial Prelature of Vila Rondônia was established (from Territorial Prelature of Guajará-Mirim and Territorial Prelature of Porto Velho and became suffragan of Manaus) |
| 1978.01.16 |  Dominican Republic | Diocese of Mao–Monte Cristi was established (from Diocese of Santiago de los Caballeros) |
| 1978.01.16 | Dominican Republic | Diocese of San Francisco de Macorís was established (from Diocese of La Vega and Diocese of Santiago de los Caballeros) |
| 1978.01.16 | Dominican Republic | Diocese of Santiago de los Caballeros lost territory to Diocese of La Vega |
| 1978.01.18 |  Germany | Diocese of Rottenburg was renamed as Diocese of Rottenburg–Stuttgart |
| 1978.01.30 |  Kenya | Apostolic Prefecture of Lodwar was promoted as Diocese of Lodwar (became suffragan of Nairobi) |
| 1978.02.27 |  Central African Republic | Diocese of Bouar was established (from Diocese of Berbérati and became suffragan of Bangui) |
| 1978.02.27 | Kenya | Diocese of Kakamega was established (from Diocese of Kisumu and became suffragan of Nairobi) |
| 1978.02.27 |  South Africa | Apostolic Prefecture of Western Transvaal was promoted as Diocese of Klerksdorp (became suffragan of Pretoria) |
| 1978.04.24 |  Argentina | Apostolic Exarchate of Argentina (Ukrainian Rite) was promoted as Diocese of Santa María del Patrocinio en Buenos Aires (became suffragan of Buenos Aires) |
| 1978.05.05 | Brazil | Diocese of Cascavel was established (from Diocese of Toledo and became suffragan of Curitiba) |
| 1978.05.05 | Brazil | Diocese of Foz do Iguaçu was restored (from Diocese of Toledo and became suffragan of Curitiba) |
| 1978.05.14 | Italy | Diocese of Massa Marittima e Populonia was renamed as Diocese of Massa Marittima–Piombino |
| 1978.05.14 | Italy | Titular Episcopal See of Populonia was restored |
| 1978.05.23 | Italy | Metropolitan Archdiocese of Milano (Ambrosian Rite) lost territory to Diocese of Lodi |
| 1978.05.31 |  Czechia | Apostolic Administration of Český Těšín was suppressed (to Metropolitan Archdiocese of Olomouc) |
| 1978.05.31 |  Poland | Metropolitan Archdiocese of Wrocław lost territory to Metropolitan Archdiocese of Olomouc |
| 1978.06.05 |  Paraguay | Diocese of Carapeguá was established (from Diocese of Villarrica and became suffragan of Asunción) |
| 1978.06.05 | Paraguay | Diocese of San Pedro was established (from Diocese of Concepción and became suffragan of Asunción) |
| 1978.06.08 |  India | Diocese of Raiganj was established (from Diocese of Dumka and became suffragan of Calcutta) |
| 1978.06.22 | India | Diocese of Irinjalakuda (Syro-Malabar Rite) was established (from Diocese of Trichur and became suffragan of Ernakulam) |
| 1978.07.11 | Argentina | Diocese of San Miguel was established (from Diocese of San Martín and became suffragan of Buenos Aires) |
| 1978.07.14 |  USA | Diocese of San Bernardino was established (from Diocese of San Diego and became suffragan of Los Angeles) |
| 1978.10.28 | India | Diocese of Bathery (Syro-Malankara Rite) was established (from Diocese of Tiruvalla and became suffragan of Trivandrum) |
| 1978.11.07 | Brazil | Diocese of Itabuna was established (from Diocese of Ilhéus and became suffragan of São Salvador da Bahia) |
| 1978.11.07 | Brazil | Diocese of Jequié was established (from Diocese of Amargosa and Diocese of Vitória da Conquista and became suffragan of São Salvador da Bahia) |
| 1978.11.15 |  Kiribati,  Nauru | Diocese of Tarawa was renamed as Diocese of Tarawa, Nauru and Funafuti |
| 1978.11.15 |  Solomon Islands | Diocese of Honiara was promoted as Metropolitan Archdiocese of Honiara (with suffragan see Gizo) |
| 1978.11.21 | Italy | Diocese of Arezzo lost territory to Metropolitan Archdiocese of Siena |
| 1978.11.27 | Brazil | Diocese of Campo Grande was promoted as Metropolitan Archdiocese of Campo Grande (with suffragan sees Corumbá, Dourados, Três Lagoas and Coxim) |
| 1978.12.09 |  Philippines | Diocese of Tandag was established (from Diocese of Surigao and became suffragan of Cagayan de Oro) |
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