OBJECTIVES: This study examined patient age and gender as well as racial and geographic variations in the prevalence of cystic fibrosis (CF), a chronic lung disease common in children and young adults, in the U.S. Medicaid population.  METHODS: A retrospective study was performed among the U.S. Medicaid fee-for-service (FFS) population from 2008 through 2009. CF patients were identified using International Classification of Disease, 9^th Revision, Clinical Modification (ICD-9-CM) diagnosis code 277.0x. Patients with continuous Medicaid FFS enrollment in both 2008 and 2009 were included for analysis. Any managed care enrollment during the period was not permitted. CF prevalence was stratified by region, state, age, gender and race, for all patients and measured by number and percentage, in each category.  RESULTS: A total of 2,550 patients were diagnosed with CF among the Medicaid FFS population in 2008 and 2009. Prevalence was the highest (0.15%) for patients under age 40 years, followed by patients age 40 to 59 (0.03%), and 60+ (0.01%). CF prevalence by race was also examined, with the following results: White (0.06%), Hispanic (0.04%), Black (0.03%), Native American (0.02%) and Asian (0.02%). Male patients had a relatively higher prevalence compared to female patients (0.06% vs. 0.05%).  Geographic variation was also analyzed, and the highest CF prevalence was observed in Minnesota (0.16%), followed by Ohio, Maryland, North Dakota (all at 0.11%) and West Virginia (0.09%). Patients residing in the Midwest had the highest prevalence rate (0.07%), compared to the Northeast (0.05%), South (0.04%) and West (0.03%).  CONCLUSIONS: Statistical evidence shows that younger patients have a higher probability of being diagnosed with CF, with white patients more likely to be diagnosed with CF compared to those of other races. Male patients who resided in the Midwest U.S. region were also found to be at higher risk for a CF diagnosis.