Durasphere is gaining popularity as a bulking agent for treating women with stress urinary incontinence. We present a series of patients with periurethral mass formation following Durasphere injection. The charts of 135 women with a mean age of 69.4 years (range 46 to 83) who underwent Durasphere periurethral injections were retrospectively reviewed. Patients who had a periurethral mass were identified and their clinical data were collected and analyzed. Four patients (2.9%) were diagnosed with periurethral mass formation 12 to 18 months (average 14.7) following a Durasphere injection. Clinical presentation varied, including irritative voiding symptoms, pelvic pain and urinary incontinence. All patients were found to have a tender and tense periurethral mass. A radiopaque mass was revealed during videourodynamic study in 1 patient. Incision, and transvaginal and endoscopic drainage or transvaginal excision were used to treat these masses. Intraoperative and pathological findings as well as operative outcomes are presented. Irritative or obstructing voiding symptoms, pelvic pain or a periurethral mass in patients with a history of Durasphere or other periurethral bulking agent injection should alert the physician to the possibility of periurethral mass formation. The true incidence of this late complication remains to be determined.