The accuracy of ultrasound in predicting the extent of local tumour spread through the rectal wall and in identifying involved perirectal lymph nodes was evaluated prospectively in 25 patients with rectal cancer. For each patient, the ultrasonic appearances recorded on videotape were compared with operative findings and/or the histology of the tumour. The extent of direct spread was classified into four curable and two incurable categories and was correctly predicted in 20 of 25 patients (80% accuracy). Lymph node status was correctly predicted in 16 of 20 patients (80% accuracy). These results suggest that pre‐operative assessment of patients with rectal cancer using transrectal ultrasound is a useful technique which may assist the surgeon in his choice of operation and in the selection of those patients who may benefit from pre‐operative radiother