A urologist in Phoenixville, Pennsylvania, noted an apparent excess of invasive bladder cancer cases in his practice area during 1988 and 1989. Background incidence data for the local area were derived from state Cancer Registry statistics. Seventeen additional cases were noted during review of local hospital tumor registry data. Exposure evaluation included complete occupational histories for 15 index cases and correlation of residential histories with a review of local industries, water quality data, and toxic waste sites. The data were compared with incidence data from 1984 and 1985, and no increase in bladder cancer incidence for this area in 1988 and 1989 was evident. There was, however, a higher bladder cancer incidence among white males in the study area and Chester County, compared with Pennsylvania as a whole. Residential histories and environmental analysis did not reveal a common environmental carcinogen. A high incidence of occupational exposure to suspected bladder carcinogens was noted. In addition, all but 4 of the index cases smoked cigarettes. The study was limited by an extreme paucity of water supply analysis data. Effective environmental monitoring would promote more effective research into environmental carcinogenesis.