Assessment of the performance of primary care physicians requires multiple, reliable measures. This article explores the appropriateness of selected Health Plan Employer Data and Information Set (HEDIS) measures, developed to assess health plans, to assess individual physician performance. To determine the consistency and reliability of 4 measures of primary care physician performance measures: cancer screening, diabetic management, patient satisfaction, and ambulatory costs. The study population consisted of all 194 family practitioners and general internists providing ambulatory services in 1998 to a defined patient panel of 320,000 adult health maintenance organization members. Administrative data on physician practice and performance were assessed with multiple regression and analysis of variance. Each performance measure was significantly related to 1 or 2 of the other measures: high cancer screening rates with good diabetic management and high patient satisfaction, good diabetic management with high cancer screening rates, high patient satisfaction with high cancer screening rates and high ambulatory costs, or high ambulatory costs with higher patient satisfaction. Although 76% of the physicians ranked in the highest third for at least 1 measure, 81% of these high performers ranked in the lower third for at least 1 other measure. Three percent of physicians ranked exclusively in the top or bottom third on all measures. Care should be taken in assessing physicians based on narrow performance measures. Assessments of individual physicians with current performance measures might identify areas in which improvement is needed and to provide feedback to improve performance quality and efficiency. However, assumptions should not be made from one measure of performance to another.