A multivariate analysis was performed on data from 221 patients with superficial bladder tumors (papilloma in 30, grade II to III stage Ta in 51, grade II to III stage Tis in 111 and grade II to III stage T1 in 29) who were treated with intravesical bacillus Calmette-Guerin and followed for a minimum of 24 months or until progression. The purpose of this analysis was to identify prognostic variables predictive of tumor progression defined as muscle invasion, metastasis or endoscopically uncontrolled superficial bladder carcinoma involving the bladder and/or prostatic urethra. Variables examined before bacillus Calmette-Guerin, and at 3 and 6 months after bacillus Calmette-Guerin included age, sex, race, purified protein derivative reaction, duration of disease, tumor category, tumor grade, multifocality, results of cytology, flow cytometry, cystoscopy, biopsy, prior chemotherapy and bacillus Calmette-Guerin treatment regimen. Significant variables (Cox regression analysis, p less than 0.07) for tumor progression were before bacillus Calmette-Guerin--stage T1 tumors and duration of disease less than 1 year, at 3 months after bacillus Calmette-Guerin--stage T1 tumor, duration of disease less than 1 year, positive cytology studies and multifocality, and at 6 months after bacillus Calmette-Guerin--stage T1 tumor, positive cytology and positive biopsy other than stage T1 tumors. Prognostic risk groups were best defined at 6 months after bacillus Calmette-Guerin, the probability of tumor progression thereafter being at 1, 3 and 5 years, respectively, as follows: for risk group 1 (T1 tumor)--71, 100 and 100 per cent, for risk group 2 (positive biopsy other than T1 plus positive cytology)--25, 79 and 100 per cent, for risk group 3 (either positive biopsy other than stage T1 or positive cytology studies)--18, 40 and greater than 81 per cent, and for risk group 4 (negative biopsy and negative cytology studies)--2, 11 and 26 per cent, respectively. Evaluation of patients with superficial bladder carcinoma at 6 months after intravesical bacillus Calmette-Guerin therapy identifies the probability of tumor progression. Patients at high risk for tumor progression require alternative treatment strategies, whereas low risk patients can be observed for further therapy if necessary.