The authors retrospectively reviewed a series of bladder wash cytologic specimens and concurrently available bladder biopsy samples to evaluate granulomatous inflammation in patients receiving intravesical bacillus Calmette-Guerin (BCG) immunotherapy for transitional cell carcinoma of the bladder. Comparisons were made during the 2-month period following six weekly BCG instillations in 25 patients and during the 1-year period following the last dose of BCG in 23 patients. At some point during the 2-month follow-up period, cytologic specimens contained free histiocytes in 64%, histiocyte aggregates (resembling fragments of granulomas) in 76%, and multinucleated histiocytic giant cells in 56% of patients. Similarly, concurrent biopsy samples contained granulomas in 78% and multinucleated giant cells in 56% of patients. During the 1-year period following the last dose of BCG, inflammatory changes peaked within the first 3 months and gradually resolved at 9-12 months. In none of these instances were the cytologic features of granulomatous inflammation misinterpreted as malignant. It was concluded that the cytologic findings after intravesical BCG are more specific than previously realized and closely parallel the histologic changes seen in corresponding bladder biopsy specimens.