We studied 44 cases of small cell bladder carcinoma (SCBC) and 2 cases of large cell neuroendocrine bladder carcinoma (LCNBC) to determine the immunohistochemical profile and biologic behavior. Thyroid transcription factor (TTF)-1, cytokeratin (CK)20, chromogranin A (CgA), synaptophysin, neuron-specific enolase (NSE), and Leu-7 studies were performed. TTF-1+ cases were stained for surfactant protein A (SP-A). The immunohistochemical profile for 44 SCBC cases was as follows: TTF-1+, 11 (25%); CK20+, 3 (7%); CgA+, 13 (30%); synaptophysin+, 22 (50%); NSE+, 35 (80%); and Leu-7+, 30 (68%), and for 2 LCNBC cases was as follows: TTF-1+, 2 (100%); CgA+, (50%); synaptophysin+, 1 (50%); NSE+, 2 (100%); and Leu- 7+, 2 (100%). All cases with TTF-1 expression were negative for SP-A, except 1 case. This case was a mixed SCBC with TTF-1 expression in the urothelial component, which also expressed SP-A. Immunohistochemical markers were not associated with survival. The prognosis of SCBC is relatively better than its pulmonary counterpart. LCNBC seems to be a rarely recognized entity. TTF-1 expression is not limited to small cell lung carcinoma.