Severe dysplasia was studied in totally embedded radical prostatectomy specimens from 40 Stage B, intermediate-grade prostate cancers. All 40 cases had severe dysplasia which varied in amount (extensive in 35% of cases; intermediate in 55%; minimal in 10%). Severe dysplasia was predominantly concentrated in peripheral and posterior regions of the gland. Those cases with extensive severe dysplasia had more multifocal small cancers (14.6/case) compared with cases with intermediate (7.5/case) or minimal severe dysplasia (5.5/case). Most dominant tumor nodules had some intermingled severe dysplasia, and in 30% of the dominant tumor nodules, intermingled severe dysplasia occupied between 10% and 25% of the tumor nodule. Severe dysplasia was located next to the dominant tumor nodule in all cases. Nineteen percent of dominant tumor nodules had extensive adjacent severe dysplasia ranging from 5 to 14 mm in maximum diameter, showing that the potential exists for needle biopsy of prostate cancers to obtain only severe dysplasia. These data show a close relationship between severe dysplasia and Stage B cancers. In contrast, centrally located low-grade multifocal cancers, as seen in Stage A (incidental) carcinoma, had a significantly weaker association with severe dysplasia as compared with central, intermediate-grade, multifocal tumors or peripheral multifocal tumors of any grade.