OBJECTIVE: To compare specialist and primary care physician participation in California's Medicaid fee-for-service and managed care programs.DESIGN: Cross-sectional survey.PARTICIPANTS: A probability sample stratified by county and by race of 962 specialist physicians and 713 primary care physicians practicing in the 13 largest counties in California in 1998.MEASUREMENTS AND ANALYSIS: We used physician self-report from mailed questionnaires to compare acceptance of new Medicaid and new Medicaid managed care patients by specialists versus primary care physicians and by physician demographics, practice setting, attitudes toward Medicaid patients, and attitudes toward Medicaid managed care. We analyzed results using logistic regression with data weighted to represent the total population of primary care and specialist physicians in the 13 counties.MAIN RESULTS: Specialists were as likely as primary care physicians to have any Medicaid patients in their practices (56% vs 56%; P = .9). Among physicians accepting any new patients, specialists were more likely than primary care physicians to be taking new Medicaid patients but were significantly more likely to limit their acceptance to only Medicaid fee-for-service patients. Thus, specialists were much less likely than primary care physicians to accept new Medicaid managed care patients. After controlling for physician demographics, practice settings, and attitudes toward Medicaid patients and Medicaid managed care, specialists remained much less likely to accept new Medicaid managed care patients.CONCLUSIONS: Expansion of Medicaid managed care may decrease access to specialists as specialists were less likely to accept new Medicaid managed care patients compared to Medicaid fee-for-service patients. Any decrease in access may be mitigated if states are able to contract with group model HMOs and to recruit minority physicians.