The pedicled rectus femoris muscle and myocutaneous flap has found application for a variety of soft tissue defects of the groin, pelvis, and lower abdomen. Although a number of authors have discussed the usefulness of this muscle flap, few have documented the morbidity from loss of this muscle in the leg. We have studied 7 patients who underwent unilateral rectus femoris muscle transfer, comparing strength of the donor knee to the normal knee. All patients were studied using a computerized dynamometer for strength of knee flexion and contraction. We found that loss of the rectus femoris in patients not undergoing a postoperative program of therapy led to an average decrease in strength about the knee of 24% to 28%, depending on the motion measured. A single patient who underwent an intensive postoperative therapy program had return of normal strength in his donor leg. Despite this common loss of strength, patient complaints were few and the results of reconstruction appeared to outweigh this loss of strength.