Thirty-seven patients with rectal villous tumours were investigated by endorectal sonography to assess the integrity of the rectal muscularis propria at the tumour level. In four cases assessment of invasion was impossible. In 24 patients, endosonography revealed an ultrasonically superficial lesion not infiltrating the muscular layer. This was confirmed either, in the case of laser treatment, by the absence of malignant recurrence during the follow-up period or by histological examination after surgical resection. In nine patients, endosonography showed infiltration of the muscular layer. This was histologically confirmed in five operated patients. In the remaining four, laser destruction was performed: in two, a rectal adenocarcinoma was present 3 and 6 months later, respectively. These findings show that endosonography has a place in the management of rectal villous tumours, demonstrating invasive cancer in cases where other forms of assessment were wrongly reassuring.