The diagnosis of carcinoma in situ of urinary bladder is difficult in that the symptoms and cystoscopic findings are nonspecific. The cytology of urine could be helpful for diagnosis of carcinoma in situ of urinary bladder. We present a case of bladder washing cytology of carcinoma in situ. A 54-year-old man presented with dysuria for 1 year. Cystoscopic findings revealed multifocal reddish trabeculated lesions. The bladder washing cytology revealed rather uniform tumor cells which were singly scattered of forming syncytium in the clean back-ground. The nuclei were round to oval with inconspicious nucleoli. The cystoscopic biopsy revealed typical histologic features of carcinoma in situ of urinary bladder.