The combined histologic and cytologic grading of carcinomas of the prostate is not only important in evaluation of prognosis but determines the choice of therapy with knowledge of staging. Tissue biopsies of 2,200 prostatic carcinomas were classified and graded histologically and cytologically. Furthermore, autoradiographic studies were performed on 69 needle biopsies with 3H-thymidine. The cytologic parameters were correlated with cell-kinetic parameters in classification. Several subgroups of degrees of malignancy were found. Grade la corresponds to highly differentiated glandular carcinomas by histology and cytology. Grade lb carcinomas were histologically well but cytologically moderately differentiated. Grade IIa carcinomas are histologically moderately to poorly but cytologically moderately differentiated. Grade IIb carcinomas correspond to poorly differentiated tumors by histological and cytological criteria. Grade III carcinomas are in most cases undifferentiated. This differentiated grading is particularly important for therapeutic consequences in incidental carcinomas. The therapeutic consequences of grade la carcinomas are frequent controls and a wait-and-see attitude. Grade lb and IIa carcinomas must be treated according to their clinical stage by total prostatectomy. Grade lib and III carcinomas need a palliative treatment by hormones, castration, irradiation or cytostatic drugs.