The Diocese of Ischia () is a Roman Catholic ecclesiastical territory in Campania, southern Italy. It is a suffragan of the Archdiocese of Naples. The diocese comprises the entire island of Ischia, which contains seven communes divided into two circumscriptions. In 1743, the population was about 4,000. The city of Ischia constituted one single parish, with two religious houses of men and one of women. In 2018, the population of the town of Ischia was 20,118.