The objective of this study is to compare the performance of Medicaid health maintenance organizations (HMOs) and fee-for-service (FFS) Medicaid regarding the prevalence of potentially preventable hospitalizations, a recognized measure of outpatient care quality.This study used nationally representative data on non-institutionalized Medicaid recipients, ages 18-64, from the 2003-2012 Medical Expenditure Panel Survey. Separate analyses are conducted for recipients insured through both Medicaid and Medicare ("dual eligibles") and recipients whose only health insurance is Medicaid ("non-duals"). In each group the occurrence of potentially preventable hospitalizations is measured, and then survey-weighted multivariable logistic regression models are fit to quantify the relationship between Medicaid HMO status and the occurrence of such stays. The possibility of selection bias into HMOs is considered and explicitly addressed in model estimation using propensity score methods.Adjusting for covariates and confounders dual eligible enrolled in Medicaid managed care are more likely to have a potentially preventable hospitalization relative to those covered under FFS Medicaid (survey weighted logit model OR = 1.72, 95% CI = 0.98-3.03; propensity score weighted logit model OR = 1.87, 95% CI = 1.06-3.28). In contrast, the odds ratios did not differ among non-duals in Medicaid HMOs versus FFS Medicaid.These findings suggest that, at least for dual eligibles, the quality of outpatient care in Medicaid HMOs may be worse than under FFS Medicaid. Better and more streamlined clinical preventive approaches for this high risk and vulnerable population might be required in Medicaid HMOs.