Various benign conditions have been found to cause hypoechoic lesions in the prostate gland, thus mimicking the sonographic appearance of early prostatic cancer. Transrectal sonograms in a large series of patients with biopsy-proved clinical stage B prostatic cancer were retrospectively reviewed to determine the pathologic correlate to benign hypoechoic peripheral zone lesions. Transrectal sonograms demonstrated hypoechoic lesions that did not represent cancer in 25 of 160 patients examined. All lesions were contralateral to the carcinoma. Pathologic correlation was found in 24 of the 25 lesions. The results of this study show that contralateral hypoechoic lesions in patients with pathologically proved prostatic cancer do not necessarily imply bilateral tumor involvement; they accounted for benign lesions that mimicked the sonographic appearance of malignant tumors and thus produced a false-positive rate for cancer in the contralateral lobe of 16% of patients (25 of 160) with clinical stage B cancer.