Objective: To examine the incidence of childhood type 1 diabetes in Western Australia from 1985–2010.

Research Design and Methods: Incidence rates were calculated for children aged 0–14 years and were analyzed by calendar year, sex, and age at diagnosis.

Results: There were 1,873 cases, and the mean incidence was 18.1/100,000 person-years (95% CI: 17.5–19.2). The incidence increased by 2.3% a year (1.6–2.9%) with a sinusoidal 5-year cyclical variation of 14% (7–22%). The lowest rate of increase in incidence was observed in 0–4-year-olds.

Conclusions: The cyclical pattern in incidence observed supports the role of environmental factors in childhood type 1 diabetes.