We assessed improvement of preventive health care behaviors by physicians in an independent practice association-health maintenance organization. A before-after, 3-year study of a defined cohort measured changes through chart audit, accompanied by peer review, feedback, and financial incentives. Outcome measures consisted of rates of mump-measles-rubella (MMR) immunization, screening for cholesterol levels, and charting adequacy. Offices meeting MMR vaccination standards over 3 years increased from 78% to 96% (P < .05); those meeting standards for screening for cholesterol levels, from 92% to 95%. The average scores for charting adequacy rose from 87% to 92% (P < .05). The percentage of practices not in compliance with a standard of 90% decreased as follows: for MMR vaccination, from 57% to 12%; for screening for cholesterol levels, from 21% to 11%; and for charting adequacy, from 53% to 29% (P < .05).