Quality assurance is required of all hospital outpatient clinics although there is little evidence documenting its value. The purposes of this study were to assess the impact of quality assurance audits on physicians' ordering behavior and to learn whether doctors who actually performed audits behaved differently from physicians who passively received audit results. Baseline influenza vaccination and screening mammography ordering rates were established for the authors' residents' clinic in 1985. In 1986, residents were assigned randomly to three groups. Residents in one group audited their own charts for 1985 influenza vaccination ordering; the second group audited its own charts for 1985 screening mammography ordering; and the third group performed no audit but received the other groups' results. Passive receipt of results improved ordering of vaccination from 40% to 59% and ordering of mammography from 8% to 16%. Actual performance of audits improved ordering of mammography from 16% to 26% but did not improve vaccination ordering. These quality assurance audits were effective in improving the performance of selected preventive health measures in a residents' clinic.