A series of 157 patients with prostate cancer underwent transrectal ultrasonography prior to radical prostatectomy. In 112 patients (71.3%) the tumours appeared hypoechoic relative to the echo pattern of the normal peripheral zone; in 43 (27.4%) they appeared isoechoic, and in only 2 (1.3%) did they appear purely or predominantly hyperechoic. These 2 hyperechoic tumours were unusual ductal adenocarcinomas with central necrosis and dystrophic calcification within solid tumour nests, a pattern similar to that of comedo-carcinoma of the breast. Calcification within prostate cancer was found in 4 of the 157 radical prostatectomy specimens, including 2 other hypoechoic cancers which contained intraluminal or psammomatous calcification. Although the most common sonographic appearance of localised prostate cancer is hypoechoic, a predominantly hyperechoic pattern is seen occasionally and suggests the presence of a high grade ductal adenocarcinoma.