Purpose: We evaluated the effectiveness of periurethral autologous fat injection as treatment for female stress urinary incontinence. Materials and Methods: Women with stress incontinence were randomized in a double-blind fashion to receive periurethral injections of autologous fat (treatment group) or saline (placebo group). After injection patients were evaluated monthly for 3 months by a validated standardized incontinence questionnaire, 1-hour pad test and cough test. Patients who remained incontinent were offered repeat injection using the same initial agent to a maximum of 3 injections. Every 3 months after injection patients were assessed by a standardized questionnaire, pad test, cough test and urodynamics. Those who did not qualify for repeat injection at 3 months were then followed 6, 9, 12, 18 and 24 months or until failure. Results: Of the 68 women enrolled 35 received fat and 33 received saline injections. The groups were comparable in terms of baseline parameters. A total of 56 patients completed the study, including 27 in the fat and 29 in the placebo group, for a total of 189 injections (91 fat and 98 saline). At 3 months 6 of 27 (22.2%) and 6 of 29 (20.7%) women were cured or improved in the fat and saline groups, respectively. Complications included cystitis in 9 of 189 injections, urinary retention in 6 in the fat injection group, urge incontinence in 9 of 68 patients and pulmonary fat embolism resulting in death in 1 of 189 procedures. Conclusions: In this study periurethral fat injection did not appear to be more efficacious than placebo for treating stress incontinence.