The stapler treatment first described by Longo is considered by some authors to be a good technical solution for mucohaemorrhoidectomy. The aim of the present prospective study was to assess the function and morphology of the internal and external anal sphincters preoperatively and one month after surgery by means of a clinical examination, anorectal manometry and transperineal ultrasound. Ten patients (6 M, 4 F) underwent rectal mucosal prolapsectomy according to Longo. Anoscopy, anorectal manometry and transperineal ultrasound were performed in all patients preoperatively and again one month after surgery. The thickness and integrity of the internal and external anal sphincters were ascertained and colour Doppler was performed to assess the presence, quantity and size of any haemorrhoid swellings. All anatomical specimens underwent histological examination in search of smooth muscle fibres. Anorectal manometry revealed no postoperative sphincter tone defects. Transperineal ultrasound detected no postoperative sphincter lesions and the presence of venous swellings (always present at preoperative colour Doppler) never persisted at postoperative follow-up. The mean follow-up was 52.7 days (range: 31-151). Transperineal ultrasound proved useful in demonstrating the lifting of the mucohaemorrhoid prolapse within the ampulla of the rectum one month after surgery. The Longo procedure, in our albeit limited experience, caused no sphincter lesions.