Twenty-eight patients with prostatic carcinoma who underwent magnetic resonance (MR) imaging and subsequent radical prostatectomy were studied. The resected prostates were sectioned axially, and the whole-mount prostatic specimen was compared with the corresponding MR images. The carcinoma could be identified in 20 cases (71%), but the tumor volume was underestimated in 12 patients (43%). In 19 of 20 visualized cases (95%), the carcinoma was seen as an area of low signal intensity within the peripheral zone on T2-weighted images. However, in one case the signal intensity of the carcinoma was higher than that of the remainder of the peripheral zone. All carcinomas were located within the peripheral zone. The accuracy of MR imaging in the prediction of extraglandular tumor spread was 82%, with a sensitivity of 37.5% and a specificity of 100%. Nineteen patients (67%) exhibited histologically benign hyperplasia, which could be identified on MR images in 10 cases (53%). The signal intensities of the nodules varied. All areas of benign hyperplasia were located within the central zone. The location of the pathologic changes must therefore be considered in differential diagnosis.