Health maintenance organizations (HMOs) are providing an increasing proportion of medical care in the United States. Characteristics of these organizations such as cost containment, incentives to reduce spending by practitioners, and barriers to access for clients raise significant ethical concerns. This paper considers how these features of the HMO withstand ethical scrutiny and what may be done to prevent abuse. Generally, the challenges to the moral integrity of physicians practicing in HMOs are neither intractable nor in all cases unique, although special arrangements may have to be made to ensure that ethical standards are upheld. Independent practice associations pose particular problems. Finally, whether or not an HMO is a for-profit enterprise is a significant consideration.