['Substaging of T1 bladder tumors into T1a and T1b based on invasion of the tumor superficial to and beyond the muscularis mucosa has been assigned prognostic significance. We determined whether outcomes after intravesical bacillus Calmette-Guerin (BCG) differ between stage T1a and T1b subcategories.', 'Retrospective pathological evaluation of the initial transurethral resection specimens of stage T1 bladder tumors was performed by 2 pathologists. Grade 1, 2 or 3 and stage T1a or T1b were assigned to each case. Followup was from the date of transurethral resection to date of death or the last visit. Kaplan-Meier probability and log rank test were used to evaluate recurrence and progression.', 'Substaging was performed in 49 of the 55 patients (89%) with stage T1 disease. Disease was stage T1a in 32 (65%), stage T1b in 17 (35%), grade 3 in 45 (92%) and grade 2 in 4 (8%) cases. Maximum followup was 147 months (median 71) and 28 cases had a minimum of 5 years of followup. Recurrence was noted in 33 cases (67.3%), including 22 stage T1a (69%) and 11 stage T1b (65%), at a median followup of 11.3 and 8.6 months, respectively. Progression to a higher stage of disease was recorded in 12 cases (24.4%), including 7 (22%) stage T1a and 5 (29%) stage T1b, at a median followup of 108 and 120 months, respectively. The difference between T1a and T1b subcategories was not statistically significant in regard to recurrence-free (p = 0.7203) and progression-free (p = 0.574) outcomes.'] Are outcomes after intravesical bacillus Calmette-Guerin affected by substaging of high grade T1 transitional cell carcinoma?