A new histologic grading system for prostatic adenocarcinomas is presented, and its clinical significance tested. Histologic growth patterns and nuclear anaplasia found therein are evaluated independently of each other. The diagnostic categories are in accordance with the histologic classification recently published by the WHO.29 The tumor is denominated according to the least differentiated fraction. Three grades of malignancy, which correspond to significantly different survival probabilities, are distinguished. The prognosis of grade 1 patients is not reduced in comparison to that of healthy males of the same age. Grade 1 patients did not reveal metastases. The rate of tumor‐specific deaths increases with the malignancy grade of the tumor. Interobserver reproducibility of this grading is found to be 91%. With 5% undergradings, the representativity is found to be satisfactory. Prostatic carcinomas tend to change their malignancy grades in time. The question of whether grade I prostatic carcinoma patients with early clinical stages benefit from therapy is discussed.