Bladder pathologic features related to intravesical bacillus Calmette-Guerin (BCG) therapy in superficial bladder cancer (Ta, T1, Tis) were evaluated and related to clinical outcome. A total of 105 patients were treated with 75 mg Pasteur BCG weekly for six consecutive weeks. When tumor was not demonstrated a maintenance course was given. An additional six-week course was given when tumor recurrence or persistence, without progression, was observed after the induction course. An inflammatory change in the bladder was the most common pathologic finding. Granuloma was the only specific BCG-related feature and did not appear to be a prognostic factor because of low incidence (24%) and lack of correlation with clinical course. Dysplasia occurred more frequently (57%) in nonresponder patients and (26%) in responder patients, often heralding recurrence of tumor. All patients showing concurrent squamous and/or glandular metaplasia were unresponsive to BCG therapy. Histology and cytology did not correlate perfectly: cytology was ineffective in low-grade tumors and improved diagnostic accuracy, particularly when dysplasia was histologically evident.