SUMMARY Four hundred fifty seven cases of bladder neoplasm were reviewed according to criteria which emphasized both intracellular and intercellular architectural features. The material represented the initial biopsy or surgical specimen in over 90 per cent of cases. There were 338 males and 110 females (2.8:1) in the series. Invasion of subepithelial connective tissue or of the lamina propria was found in 267 initial specimens. Transitional cell neoplasms constituted 76 per cent of the series. Only two lesions were diagnosed as papilloma, an entity which we defined as a noninvasive papillary lesion covered by normal transitional cell epithelium. As so defined this is a rare lesion in the experience of the surgical pathologist. Transitional cell carcinomas were graded on the degree of nuclear anaplasia and cytoplasmic differentiation. Invasion of subepithelial tissue was present in only 6 per cent (5 of 79) of Grade 1 lesions, and was of minimal degree—involving only subepithelial fibrovascular tissue—in those cases. Invasion was present in 52 per cent of the Grade 2 lesions and 82 per cent of those classified as Grade 3. For noninvasive papillary transitional cell lesions we favor the term papillary transitional cell carcinoma in-situ, together with the appropriate histologic grade. The latter is based primarily on nuclear appearance. Squamous lesions made up 13 per cent of the total cases, our criteria for diagnosis being less restrictive than those used by other authors. Papillary in-situ squamous carcinomas were also seen. Flat carcinoma in-situ, a lesion with a marked qualitative abnormality but little quantitative epithelial change, was noted in both the squamous and transitional cell categories. Six per cent of the carcinomas were of mixed histologic type with two or more tissue patterns being represented. A combined transitional cellsquamous lesion was the commonest, followed by a transitional cellglandular pattern. We prefer to use the purely descriptive term “mixed carcinoma” to indicate the presence of so-called metaplastic areas. Small numbers of pure adenocarcinomas, sarcomas, and undifferentiated carcinomas completed the series.