BACKGROUND The management of transitional bladder cancer, which invades the lamina propria (pT1) and has a marked propensity for recurrence and progression, is controversial. Without adjuvant treatment the recurrence rate can be up to 80% and progression up to 50%. We retrospectively analyzed the incidence of recurrence and progression of pT1 transitional bladder cancer (grade 1-3) after complete transurethral resection of a bladder tumor (TURBT) and adjuvant immunotherapy with bacillus Calmette-Guérin (BCG). METHODS 77 patients with stage pT1 transitional cell carcinoma underwent TURBT of all visible tumors and adjuvant BCG intravesical instillations. Before BCG therapy, 12 patients presented with stage pT1 G1 tumors, 50 presented with pT1, and 15 with pT1 G3 tumors. RESULTS 51 patients (66.2%) were disease-free throughout the BCG instillation and follow-up period (median of 45 months); 8 patients (10.4%) experienced recurrence during the BCG instillations, but were disease-free following the last instillation; 16 patients (20.8%) experienced recurrence at a median of 17 months, and 2 patients (2.6%) with pT1 G3 died because of progression. CONCLUSIONS Adjuvant intravesical BCG therapy following TURBT appears to be an effective primary treatment for patients with pT1 transitional cell carcinoma.