PURPOSE: Bacillus Calmette-Guerin (BCG) therapy is considered to be an effective prophylactic and therapeutic agent for high risk superficial transitional cell carcinoma of the bladder. Nevertheless, in a select uncommon population of stage Ta grade 3 superficial lamina-free tumors the results of this treatment have not yet been well established. We evaluated recurrence and progression rates, and the success of BCG therapy in a population with stage Ta grade 3 transitional cell carcinoma of the bladder. MATERIALS AND METHODS: Of the 605 patients treated at our institution from 1982 to 1996 for the histopathological diagnosis of primary bladder cancer 32 (5.3%) with stage Ta grade 3 noninvasive primary bladder tumor were treated with intravesical instillations of 75 mg. Pasteur strain BCG in 50 ml. saline weekly for 6 weeks. At a followup of 2 to 13 years (mean 58.4 months) patients were evaluated with urinary cytology, cystoscopy, transurethral resection and random mucosal biopsies. Recurrence, grade and stage progression, death and causality were analyzed. RESULTS: Of the 32 patients 9 (28%) responded positively to BCG without recurrence, while disease recurred as stage Ta in 8 (25%) and T1 in 7 (22%), and progressed to muscle layer infiltration in 8 (25%). Four patients (12%) died of bladder cancer. The number of tumors at primary resection, gross examination, the mitotic index or an association with carcinoma in situ did not appear to be predictive factors of progression to muscle invasion. Urine cytology (I to II versus III to IV) appeared to correlate highly with progression and BCG response (p<0.001) with excellent sensitivity (1) but low specificity (0.67). CONCLUSIONS: Our study demonstrates the high progression potential of stage Ta grade 3 tumors, since nearly 50% recurred and 25% progressed to invasive disease. These results may be closely compared with the results of previous trials of stage T1 grade 3 disease. We suggest that recurrence should be detected at an early stage using long-term followup with strict observance of the surveillance protocols during a minimum 5-year tumor-free period.