Background: In 2007 the Centers for Disease Control and Prevention (CDC) reported a higher prevalence of autism spectrum disorder (ASD) in New Jersey, one of the wealthiest states in the United States, than in other surveillance regions. Objective: To examine the association of socioeconomic status (SES) with ASD prevalence. Methods: Information on eight-year-olds with ASD from four counties was abstracted from school and medical records. US Census 2000 provided population and median household income data. Results: 586 children with ASD were identified: autism prevalence was 10.2/1000, higher in boys than girls (16 vs. 4/1000); higher in white and Asian non-Hispanics than in black non-Hispanics and Hispanics (12.5, 14.0, 9.0, and 8.5/1000, respectively); and higher (17.2/1000 (95% CI 14.0-21.1)) in tracts with median income greater than US$90,000 than in tracts with median income [less than or equal to]US$30,000 (7.1 (95% CI 5.7-8.9)). Number of professional evaluations was higher, and age at diagnosis younger, in higher income tracts (p less than 0.001), but both measures spanned a wide overlapping range in all SES levels. In multivariable models race/ethnicity did not predict ASD, but the prevalence ratio was 2.2 (95% CI 1.5-3.1) when comparing highest with lowest income tracts. Conclusions: In the US state of New Jersey, ASD prevalence is higher in wealthier census tracts, perhaps due to differential access to pediatric and developmental services. (Contains 3 tables and 1 figure.)