OBJECTIVES: The current study examined patient age, gender, race, geographic variation as well as the prevalence of autism in children using U.S. Medicaid data.  METHODS: A retrospective study was performed among the Medicaid fee-for-service (FFS) population from January 1, 2008 through December 31, 2009. Children under age 17 years and diagnosed with autism were identified using International Classification of Disease, 9^th Revision, Clinical Modification (ICD-9-CM) diagnosis code 299.0x. A 2-year period of continuous Medicaid FFS enrollment during the study period was required.  Disease prevalence was stratified by region, state, age, gender and race for all patients, and measured by number and percentage in each category. Patients with managed care enrollment in any month of 2008 or 2009 were excluded from the study.  RESULTS: A total of 23,589 children diagnosed with autism were analyzed. Children age 6-10 years had the highest autism prevalence level (4.59%), followed by those age 11-17 (3.62%) and 0-5 years (1.50%). Prevalence results according to race are as follows: Asian (6.33%), White (4.06%), Hispanic (3.29%) and Black (2.75%). Autism was more likely to be diagnosed among boys (5.01%) than girls (1.62%). Geographic variation analysis showed the highest autism prevalence in Idaho (34.06%), followed by Oklahoma (17.14%), Connecticut (14.05%), Minnesota (13.44%) and Rhode Island (11.33%). The Southern region of the United States was found to have the highest autism prevalence for children under age 17 (4.35%), compared to the Midwest (4.03%), Northeast (3.43%) and West (0.82%).  CONCLUSIONS: Children age 6-10 years had a higher probability of being diagnosed with autism, with Asian patients most likely to be diagnosed with autism compared to other races. Children residing in the Midwestern region of the United States were shown to be at a higher risk for an autism diagnosis.