Forty eight patients with T1 G3 bladder cancer were treated between 1975 and 1991. An associated carcinoma in situ in one third of cases. Twenty six patients received intravesical BCG instillations (an average of 2.5 courses of 6 instillations) with no local recurrence or metastases in 50% of cases (mean follow-up: 54 months). Thirteen patients developed recurrence after a mean disease-free interval of 8 months (range: 3 to 18 months: 7 with disease progression, 5 at an identical stage and 1 Ta. Six cystectomies were performed in this group over the following two years: 3 patients were cured with a mean follow-up of 33 months, 2 died from their cancer, 1 patient is alive with an urethral redux. In view of age and/or clinical context, 7 patients were treated by repeated resections and other local treatments: 3 relapsed without progression, 2 died from their cancer and 2 have been lost to follow-up. Twenty one cystectomies were performed as first-line treatment: 20 patients are recurrence-free with a mean follow-up of 47 months and one patient died from cancer within 6 months. T1 G3 bladder cancer should be considered to be a lesion with a poor prognosis, requiring active treatment. First-line BCG therapy is effective in 50% of cases, but cystectomy is required in the absence of response to BCG.