Purpose. The mini-clinical evaluation exercise, or mini-CEX, assesses residents' history and physical examination skills. To date, no study has assessed the validity of the mini-CEX (mCEX) evaluation format. The authors' objective was to determine the reliability and validity of the MCEX evaluation format. Method. Twenty-three first-year residents at Wright-Patterson Medical Center in Dayton, Ohio, were included in the study (academic years 1996-97, 1997-98, and 1998-99). Validity of the instrument was determined by comparing MCEX scores with scores from corresponding sections of a modified version of the standard American Board of Internal Medicine's (ABIM's) monthly evaluation form (MEF) and the American College of Physicians-American Society of Internal Medicine In-Training Examination (ITE). All ABIM MEFs were used without exclusionary criteria, including ABIM MEFs from months where a corresponding MCEX evaluation was not performed. Results. Each resident in the study had an average of seven MCEX evaluations and 12 ABIM MEFs. Of the 168 required MCEX evaluations, 162 were studied. Internal consistency reliability was .90. Statistically significant correlations were found for the following: MCEX history with ABIM history; MCEX physical exam with ABIM physical exam; MCEX clinical judgment with ABIM clinical judgment, medical care, medical knowledge, and the ITE; MCEX humanistic attributes with ABIM humanistic attributes, and MCEX overall clinical competence with ABIM overall clinical competence, medical care, medical knowledge, and the ITE. Analysis of variance comparing sequential mean MCEX scores yielded no significant difference. Conclusions. This study suggests that the MCEX is a feasible and reliable evaluation tool. The validity of the MCEX is supported by the strong correlations between MCEX scores and corresponding ABIM MEF scores as well as the ITE.