We studied 51 patients with superficial bladder carcinoma who had been treated with transurethral resection of all gross tumor followed by intravesical bacillus Calmette-Guerin weekly for 6 weeks. Within 72 hours of either the first or second quarterly cystoscopic surveillance examination after bacillus Calmette-Guerin therapy, a conventional cytology study was obtained. Of these patients 8 (15.7 per cent) had positive, 9 (17.6 per cent) suspicious and 34 (66.7 per cent) negative postoperative cytology studies. Subsequent tumor recurrence was defined as a positive biopsy or visible papillary tumors on cystoscopic examination. All 8 patients with a positive postoperative cytology study had tumor recurrence at a median interval of 4 months. Of the 9 patients with a suspicious study 7 (77.8 per cent) had recurrent tumor at a median interval of 7 months and 2 (22.2 per cent) had no evidence of disease at 16 and 19 months, respectively. Of the 34 patients with a negative postoperative cytology study 13 (38.2 per cent) had tumor recurrence after a median interval of 4 months and 21 (67.8 per cent) had no evidence of disease after a median of 25 months. The tumor recurrence rate in patients with a positive or suspicious postoperative cytology study was significantly greater than that of patients with a negative study (p equals 0.001, Fisher's exact test). Postoperative cytology appears to be a significant prognostic indicator following transurethral resection and intravesical bacillus Calmette-Guerin treatment of superficial bladder carcinoma.