© 2015 All rights reserved.Objective. To assess bladder toxicity of cyclophosphamide (CYC) and uroprotective effect of mesna in rheumatic diseases. Methods. Data of 1018 patients (725 women/293 men) treated with CYC were evaluated in this retrospective study. All of the following information was obtained: the cumulative CYC dose, route of CYC administration, duration of therapy, concomitant mesna usage, and hemorrhagic cystitis. Cox proportional hazard model was used for statistics. Results. We identified 17 patients (1.67%) with hemorrhagic cystitis and 2 patients (0.19%) with bladder cancer in 4224 patient-years. The median time for diagnosis to hemorrhagic cystitis was 10 months (4-48) and bladder cancer was 8 years (6-10.9). There were 583 patients (57.2%) who received mesna with intravenous CYC therapy. We observed similar incidence rate for hemorrhagic cystitis in both patient groups concomitantly treated with or without mesna [9/583 (1.5%) vs 8/425 (1.8%) respectively, p = 0.08]. Cumulative CYC dose (HR for 10-g increments 1.24, p < 0.001) was associated with hemorrhagic cystitis. Conclusion. Cumulative dose was the only risk factor for hemorrhagic cystitis in patients treated with CYC. No proof was obtained for the uroprotective effect of mesna in our cohort.