Summary Histological grading of prostatic adenocarcinoma contributes mortality rate prediction information in addition to that provided by clinical staging of the tumor. Combined staging and grading seems to identify groups of patients with favorable survival experience as measured by followup mortality data in 1,032 patients. There were no cancer deaths for the 68 patients (6.5 per cent) in the lowest prognostic categories 4 to 6. For the 302 patients (29 percent) in categories 4 to 8, the cancer death rate was so low that a serious question arises as to whether they should be subjected to any potentially dangerous treatment unless (and until) signs or symptoms develop which indicate that they are actually suffering progression of their cancer. The data for stages III and IV patients with histologically low grade cancers suggest that these patients are at no greater risk of death from cancer than most stages I and II patients for whom radical prostatectomy has been recommended (and was performed in this study). Combined staging and grading identified groups of patients at increasing intermediate risks and showed that these patients had a distinct reduction in cancer mortality rates associated with the administration of DES. The use of grading plus staging also emphasized that little information as to response to treatment can be gained from patients with cancer of high biological malignancy until some effective treatment is developed. Cancers of low biological malignancy cannot be expected to reveal significant treatment differences.