Two histopathologic grading systems for prostatic adenocarcinomas are reevaluated: the Gleason system and the Gaeta system. Two pathologists reviewed 234 specimens to assess reproducibility. Exact agreement is achieved in 88% with the Gaeta system, in 65% with the Gleason system. Nevertheless, agreement to within one score unit is achieved in 94% with the Gleason grading. One pathologist's autoreproducibility exceed 80% with either system. Actuarial survival curves and mortality index (deaths per patient-year of follow-up) provided evidence of their predictive value. Regardless of the clinical stage these two grading systems select groups of patients sharing a good, intermediate or bad prognosis but none can predict a given patient's accurate survival. The Gleason system would allow a better discrimination between poorly and highly aggressive tumors of intermediate grade.