A technique of proctocolectomy avoiding an ileostomy has been developed for patients with ulcerative colitis or polyposis coli. After excision of all diseased tissue a reservoir of terminal ileum is constructed which is brought through the rectal stump denuded of mucosa; an ileo-anal anastomosis is then carried out. Twenty-one patients (17 ulcerative colitis, 4 polyposis) have been treated and 20 followed for from 2 to 34 months (mean 13.5 months). There was no mortality but early complications occurred in 9 patients. All are currently well, with no disturbance of urinary or sexual function. Continence of faeces is complete in all during the day, but 1 patient evacuates unconsciously at night. The average frequency of evacuation is 3.8 times in 24 h. Ten patients void spontaneously. All patients tolerate a full diet and only 2 use medicaments to reduce frequency. This operation appears to be a satisfactory alternative to proctocolectomy with a permanent ileostomy.