CONTEXT Hip abductor muscle weakness is related to many lower extremity injuries. A simple procedure, the Trendelenburg test, may be used to assess hip abductor performance in patient populations. OBJECTIVE To describe the minimal detectable change (MDC) in pelvic-on-femoral (P-O-F) position of the stance limb during the Trendelenburg test. SETTING Laboratory. PARTICIPANTS 45 healthy women (28 +/- 8 years) and 45 healthy men (33 +/- 11 years). MAIN OUTCOME MEASURES P-O-F position in degrees in single-leg stance. RESULTS Baseline P-O-F position (hip adduction) was 83 degrees +/- 3 degrees with a range from 76 degrees to 94 degrees. The intratester reliability (ICC3,1) for measurement of P-O-F position using a universal goniometer was 0.58 with a standard error of measurement (SEM) of 2 degrees. The minimal detectable change (MDC) was calculated to be 4 degrees. CONCLUSIONS If a person's P-O-F position changes less than 4 degrees between measurements, then the P-O-F position is within measurement error and it can be determined that there has been no change in the performance of the hip abductor muscles when examined by the Trendelenburg test.