Background: The relationship between one-leg static standing balance (OLSSB) and patellofemoral pain syndrome (PFPS) is unknown. Hypothesis: OLSSB decreases in patients with PFPS. Design: Prospective case series. Methods: Fifty-two women with unilateral PFPS were enrolled in this study. OLSSB was evaluated with a stabilometer. Q angle was measured with a lengthened-arm universal goniometer. Lower extremity alignment was analyzed with full-length standing anteroposterior teleroentgenograms. Quadriceps and hamstring strength was measured on an isokinetic dynamometer. Results: There were significant differences in OLSSB, Q angle, and strength of quadriceps and hamstring between the symptomatic and asymptomatic sides. There was a correlation between the strength of the quadriceps and hamstring and OLSSB, while there was no correlation between OLSSB and the severity of pain, lower extremity alignment, and Q angle on the symptomatic side. Conclusions: OLSSB and quadriceps and hamstring strength decreased and Q angle increased on the symptomatic side in PFPS patients. A relationship between OLSSB and pain, Q angle, and lower extremity alignment was not detected, while there was a correlation between the strength of the quadriceps and hamstring and OLSSB. Clinical Relevance: A quadriceps and hamstring strengthening may be beneficial to improve OLSSB in patients with PFPS.