Background: In the nonacute setting, the diagnosis of pelvic instability is difficult. Patients who present with pelvic painmay have underlying instability. The purpose of the present study was to report the effectiveness of single-leg-stance radiographs in the diagnosis of pelvic instability in a consecutive series of patients presenting with pelvic pain. Methods: Thirty-eight consecutive patients (twenty-four women and fourteen men) ranging in age from eighteen to seventyeight years who presented with pelvic pain and a history of injury (twenty-seven), childbirth (seven [four primiparous and three multiparous]), or osteopenia (four) were evaluated with a visual analog scale pain score and a standard series of radiographs in an attempt to identify pelvic instability. The average time from the onset of symptoms to the evaluation was forty-one months (range, six weeks to twenty-seven years). Each patient was evaluated with supine anteroposterior, inlet, and outlet pelvic radiographs; a standing anteroposterior pelvic radiograph; and two single-leg-standing pelvic radiographs (one with the patient standing on the left leg and one with the patient standing on the right leg). A positive finding was defined as ≥0.5 cm of vertical translation measured at the symphyseal bodies between the two single-leg-stance radiographs. Results: Of the thirty-eight patients, twenty-five demonstrated pelvic instability (average, 1.98 cm; range, 0.5 to 5 cm). With the numbers available, the average visual analog scale pain score for the patients with a stable pelvis was not significantly different from that for the patients with an unstable pelvis (6.4 ± 2.9 compared with 7.3 ± 1.9; p = 0.28). Conclusions: Standing anteroposterior and single-leg-stance pelvic radiographs aid in the diagnosis of pelvic instability more effectively than dothe standard three radiographs of the pelvismade in the supine position or a standing anteroposterior radiograph of the pelvis alone. Additional studies will be needed to correlate this instability with clinical symptoms. Level of Evidence: Diagnostic Level IV. See Instructions to Authors for a complete description of levels of evidence.