One hundred patients with suspicion of prostatic disease were examined by transrectal ultrasound. Two urologists with experience in this technique performed the examination separately for each patient. In the present study the differential diagnosis between normal prostate, benign hypertrophy and prostate cancer was almost perfectly reproducible. However, prostatitis was a difficult diagnosis by transrectal ultrasound. Prostatic cysts and stones were readily recognised. Although not perfectly reproducible, the transverse dimensions of the prostatic adenomas were reasonably comparable. Measurement of the longitudinal diameter of prostatic adenomas was difficult and poorly reproducible in our hands.