The 1998–99 OHL season was the 19th season of the Ontario Hockey League. Twenty teams each played 68 games. The Belleville Bulls won the J. Ross Robertson Cup, defeating the London Knights.
The 1998–99 season was the first season to have the two Conference, four Division format, and the first season to have 20 teams. The Brampton Battalion and Mississauga IceDogs were the two expansion teams. The Brampton Battalion were placed in the Midwest Division of the Western Conference and the Mississauga IceDogs were placed in the Central Division of the Eastern Conference.