We evaluated the ability of magnetic resonance imaging (MRI) operating at 1.0 Tesla with a Helmholz pelvic surface coil to predict the pathological stage of prostate carcinoma. Radiological diagnosis was based on fast spin-echo axial T2-weighted images with and without frequency selective fat-suppression and fast spin-echo coronal T2-weighted images. Thirty-one consecutive patients (mean age 61 years, range 49 to 71 years) underwent pelvic MRI before radical prostatectomy. Correlation with whole-mount step-sections of the surgical specimens showed that the tumours were correctly localized in all but one prostate gland in which the tumour could not be seen on pelvic MRI. The transverse diameter of the visible tumour at pelvic MRI appeared to represent an approximate estimate of the true tumour dimension. Based on histopathologic whole-mount step-sections of the surgical specimens, 22 of 31 patients (71%) had tumours extending beyond the confines of the prostatic capsule. The specificity for MRI to predict capsular penetration and seminal vesicle invasion was relatively high (0.80 and 0.86, respectively). The sensitivity was acceptable for capsular penetration (0.62) but poor for seminal vesicle invasion (0.30).