PURPOSE: Relationships between sociodemographic and health plan characteristics and health plan member satisfaction with prescription drug benefits were studied. METHODS: A survey was mailed in November 2002 to a stratified random sample of 14,141 people covered by a pharmacy benefit management company (PBM) who had made at least one prescription drug claim during the second quarter of 2002. Survey recipients had commercial health insurance and were 19-64 years of age. Participants were stratified by drug benefit plan design (two-tier copayment system, three-tier copayment system, coinsurance, or closed formulary). The survey contained 39 questions covering satisfaction with the prescription drug benefit, health-related attitudes and knowledge, and experience with the benefit. Predictors of satisfaction were examined by using logistic regression with probability weights. RESULTS: A total of 3819 surveys were returned (response rate, 27%). Respondents were more likely to be mail-order pharmacy users and less likely to be enrolled in a plan with a closed formulary. Out-of-pocket costs were viewed as the most important feature of the pharmacy benefit. In the logistic regression, higher copayments, coinsurance, closed formularies, intensive managed care, large health care premiums, a recent increase in copayments, and a recent denial of coverage were associated with lower satisfaction with the prescription drug benefit. Excellent health and use of mail-order pharmacy were associated with greater satisfaction. CONCLUSION: The extent to which health plan members served by a PBM had to share drug costs was the strongest determinant of satisfaction with the prescription drug benefit.