Patients with chronic constipation may have one of several physiologic disorders, not all of which are amenable to operative therapy. The aim of this study was to test colonic and pelvic floor function preoperatively, to identify patients suitable for surgery based on these studies, and to determine operative outcome over time. Between 1987 and January 1991, 277 patients referred for severe symptoms of chronic intractable constipation underwent colon transit studies, measurement of anal canal pressures and reflexes, and measurements of anorectal angle movements and efficiency of evacuation. Balloon expulsion studies, electromyography of the pelvic floor, and defecating proctograms also were done. Based on these studies, patients were categorized as having: slow transit constipation (STC), 29 patients; pelvic floor dysfunction (PFD), 37 patients; STC + PFD, combined slow transit and pelvic floor dysfunction, 14 patients; and irritable bowel syndrome (IBS), 197 patients. Slow transit constipation patients underwent abdominal colectomy and reanastomosis. Pelvic floor dysfunction patients underwent pelvic floor retraining only. Patients with STC + PFD underwent pelvic floor retraining followed by abdominal colectomy. Irritable bowel syndrome patients were treated symptomatically. Among the 38 patients operated on (STC and STC + PFD), there was no operative mortality. Prolonged ileus developed in 13%, and small bowel obstruction occurred in 11% of patients. On follow-up, a mean of 20 months after ileorectostomy, no patient was constipated, none required a laxative, and none was incontinent. The mean number of stools per day was four. The authors concluded that a prospective evaluation of colonic and pelvic floor function reliably delineated constipated patients with slow transit, suitable for operative management, from those with pure pelvic floor dysfunction or irritable bowel syndrome, who were not. Abdominal colectomy and ileorectostomy in the slow transit patients was safe and effective, resulting in prompt and prolonged relief of constipation.