Strengthening of the vastus medialis oblique (VMO) has been advocated as a treatment for patellofemoral pain syndrome (PFPS), as weakness of this component of the quadriceps is postulated to contribute to malalignment of the patella. This study investigated the surface electromyographic activity (EMG) of the VMO relative to the vastus lateralis (VL) during five isometric exercises in eight PFPS female subjects and 19 controls. The area under the EMG curve of each muscle was normalized to the EMG area acquired while subjects performed a submaximal isometric contraction (50% of maximum voluntary contraction), and the "normalized" outcome measure was expressed as a proportion (VMO:VL). A two-factor repeated measures analysis of variance indicated no differences in the VMO:VL proportion between the control group and PFPS participants across the five exercises (p > .05). The VMO:VL proportions for medial tibial rotation and knee extension combined and knee extension alone were significantly greater than for the other three exercises (p < 0.005). Hip adduction or the combination of hip adduction and knee extension did not result in greater recruitment of the VMO compared with the VL.