This paper investigates differences between various HMO types (eg, staff model, group model, IPA model) in their access and quality of care outcomes. Several sources of evidence are analyzed, including research findings reported in the health administration literature, survey data from a random sample of 42 HMOs, and accreditation data gathered from 26 HMOs in four states. Consistent with previous research, both the random sample survey data and the accreditation data indicate that group and staff model HMOs score more favorably than IPA models in terms of the level of services provided, preventive care, and various quality of care outcomes. Data from the random sample survey indicate that IPA models score more favorably on measures of patient satisfaction and access outcomes. These findings are consistent with speculation that IPAs trade off utilization and quality controls for patient access and physician autonomy. Contrary to speculation, the effect of HMO type on access and quality may be independent of the degree to which physicians are financially and organizationally tied to the HMO.