213 patients, classified in 3 groups, were examined in a prospective trial using endorectal ultrasound. 80 patients (group A) had no anorectal disease, the endorectal ultrasound showed normal structures of the anorectum and the perirectal tissue. 80 patients (group B) suffered from Crohn's disease, 30 of them had no clinical signs, the rest of this group (50 patients) felt pain in the anal/perianal region. 83 patients (group C) had perianal abscesses or fistulas, Crohn's disease could be excluded. In all 64 perianal fistulas and 66 perianal abscesses were diagnosed. The results of the rectal-proctological examination were compared with endorectal ultrasound. 100% of the perianal abscesses could be recognized using endosonography. The digital-proctological examination revealed only 57% of perianal abscesses and 48% of perianal fistulas; the supralevatory abscesses couldn't be detected proctologically at all. By endorectal ultrasonography we obtained useful informations about localization and extension of the inflammatory process. From a therapeutic and prognostic view the endorectal ultrasound is a simple, practicable and useful method to investigate perianal and anorectal diseases.