Lv Jian-wei，Ning Ye, Leng Jing，Bo Juan-jie，Huang Yi-ran Department of Urology, Renji Hospital Affiliated to Shanghai Jiaotong University,School of Medicine,Shanghai, China Objective: To improve the efficiency of the diagnosis and the treatment of interstitial cystitis (IC) in males. We report our experience of interstitial cystitis, its differential diagnosis with chronic prostatitis (CP) and the effective treatment of hydrodistention with alkalized lignocaine instillation. Methods：From April 2008 to December 2010, a total of 100 patients with symptoms of suprapubic pain, urinary frequency and urgency that were diagnosed as having chronic prostatitis were recruited for this study. All these 100 patients received treatments for chronic prostatitis for at least 6 months with limited therapeutic responses. According to the The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) diagnostic criteria of IC, the Pelvic Pain And Urinary/Frequency (PUF) Symptom Scale (range: 0-35), and potassium sensitivity test (PST), were used to establish the diagnosis of IC. Cystoscopy under anesthesia was performed before the treatment of hydrodistention and instillation of alkalized lignocaine to confirm the diagnosis. Result: With PUF Symptom Scale (range: 035) and PST, 45 of these 100 patients were suspected to have IC. Thirty eight of 45 patients had a definitive diagnosis of IC as confirmed by cystoscopy under anesthesia and 26 patients received the treatment of hydrodistention and instillation of alkalized lignocaine twice every week for one month, once every week for the following two months, with a total 3 months’ course of treatment. 37/38 (11 patients only received hydrodistention, and one patient was lost in the follow-up)patients completed the treatment and the follow-up. At 1, 3 and 6 months after treatment, the comparison between instillation group (26 patients) and noninstillation group (11 patients) was done and the outcome showed statistical difference at all time points. Conclusion: Cystoscopy under anesthesia along with PUF Symptom Scale and PST could be a effective way for the differential diagnosis of IC and CP. Hydrodistention with alkalized lignocaine instillation showed a curative effect for IC patients in this study.