The aim of this retrospective study was to evaluate the effects and results of low-dose bacillus Calmette-Guérin (BCG) therapy on a selective high-risk population of stage T1, grade 3 (G3) bladder tumours. Recurrence and progression were also analysed. Thirty-five consecutive patients presenting with T1 G3 tumours were treated with intravesical BCG. All patients underwent complete transurethral tumour resection. A course of BCG 75 mg Pasteur strain was begun 4 weeks after the first resection of the diagnosed tumour and continued for a 6-week period. At the end of treatment, a complete urological evaluation was routinely carried out: urine cytology test, cystoscopy with bladder biopsies randomly performed, and any recurrences were resected. In cases of abnormal cytology and/or recurrence an additional course of BCG was initiated, followed by the same tests. Follow-up examination and cystoscopy or fibroscopy were conducted every 3 months for 1 year, semiannually and annually thereafter. Median follow-up was 45 months (range 10-120); 7 patients (20%) did not respond to BCG instillations. Of these patients, 5 underwent cystectomy and in 2 patients the bladder was left in place in spite of recurrence because of age (+80 years). Twenty-eight patients (80%) responded positively, 24 after one single course of BCG, and 4 patients after two courses. During follow-up, recurrence was observed in 8 cases: stage T1 G3 in 4 patients, T1 CIS (carcinoma in situ) in 2 patients, Ta G2 and Ta G1 in 2 patients. Three of these patients were treated by cystectomy and the remaining patients with transurethral resection alone or combined with additional courses of BCG. Overall, 25 patients (71%) were considered free of tumour occurrence after low-dose BCG therapy. Ten patients underwent cystectomy (29%) or remained in occurrence and 2 patients died of the disease. These results can be closely compared to the results of other trials conducted on stage T1 G3 and BCG treatment, using a different dosage and BCG protocol therapy. BCG is an effective prophylactic and therapeutic agent for T1 G3 carcinoma of the bladder responders. The identification of these responders before beginning instillations still remains a challenge.