The inter- and intraobserver variations of the histologic grading systems of prostatic carcinoma proposed by Gleason and by Böcking et al. were tested by the authors. Both grading systems have previously been shown to have good correlation with prognosis. After studying 91 cases of prostatic carcinomas, the interobserver agreements of the Gleason pattern score and the Böcking combined grade were found to be 36% and 69% respectively. Both observers regraded 31 randomly selected prostatic carcinomas. With the Gleason pattern score intraobserver agreements of 65% and 42% were found, whereas the intraobserver agreements of the Böcking combined grade were 90% and 71% respectively. Since the percentages of inter- and intraobserver agreements were higher with the system of Böcking et al., this system is recommended prior to the system of Gleason as a means of evaluating the prognosis of patients with prostatic carcinoma.