Ninety-two of a total 107 renal cell carcinomas excluding papillary, sarcomatoid and other uncommon histological types were classified into 3 groups based on architectural variations. Statistically analyses were carried out for prognostic significance. Histological criteria of 3 groups were defined as follows. Group I consists predominantly of tubular formations with characteristic cystic change. Group III shows solid proliferation without tubular formations, and Group II shows small alveolar or trabecular structures with inconspicuous tubular formations. According to the survival curves (Kaplan-Meier method), the prognosis of Group I was significantly better than II and III. Ten year survival rate of each group was 88 +/- 7.8% in Group I, 39 +/- 8.8% in Group II, and 0% in Group III. The distribution of T and V stages in the 3 groups were not significantly different. Nuclear grading of Group I and II was not so different, though high grade cases predominated in Group III. Therefore, the present grading of alveolar type renal cell carcinoma based on architectural atypia was considered to be a useful prognostic parameter.