The assessment of tumor extension in 20 patients with cancers of the prostate at a clinical stage A or B included MRI with a body coil before prostatectomy. Transverse and coronal T1-weighted sections with injections of gadopentate dimeglumine (gadolinium) and fat suppression were systematically taken to assess the vascularity of the various regions of the prostate and of the cancer, as well as the merits of such sequences for the assessment of extension. The normal, poorly vascularized peripheral area is only slightly enhanced by injection, while the transition area, which is most often hyperplastic in the age group studied, enhances heterogeneously with contrast. All cancers enhance after injection. In the assessment of extension, the major merit of gadolinium is that it allows exploration both of the vesiculodeferential junction on coronal sections and of the structure of the seminal vesicles. Thus a normal junction allows ruling out macroscopic invasion of the vesicles. In addition, gadolinium allows correcting false positive MRI findings when the areolar structure of the vesicles is preserved. Gadolinium does not provide additional evidence of extension through the capsule in comparison with T2-weighted sequences. On a whole, in our series, MRI with a body coil, associated T2-weighted sequences and T1-weighted sequences after gadolinium injection and fat suppression, has 58% sensitivity and 100% specificity for the diagnosis of stage C cancers.