Reports indicate sharp increase in prevalence of autism spectrum disorders (ASD). We aimed to assess the time trend in prevalence of ASD in Israel and describe demographic characteristics of the registered cases. We reviewed the autism registry of the Israeli Ministry of Social Affairs which includes 4,709 cases and identified 4,138 cases born between the years 1986 and 2005. Registered cases were mainly males (84.4%) and Jewish (96.6%). Prevalence data indicated an increase from 1.2 per 1,000 in those born in 1986 to 3.6 per 1,000 in 2003. Greater increase was seen in males, reaching a peak of 5.7 per 1,000, compared to 1.2 per 1,000 in females. Increased ASD prevalence was observed among Israeli children born in 1986-2005.