As a routine examination for intrapelvic organs, transrectal ultrasonotomography was performed 3,000 times on 2,331 patients from June 1976 to February 1980. In this series, 57 patients were diagnosed as prostatic cancer by transrectal ultrasonotomography and 54 (94.7%) of them were finally diagnosed as cancer by biopsy. Three hundred twenty-six patients were diagnosed as suspected prostatic cancer, and cancer was confirmed also by biopsy in 12 (3.7%) of them. Among 1,741 patients with various prostatic diseases on whom cancer was ruled out by transrectal ultrasonotomography, there were 2 (0.1%) false-negative cancer cases.