Serious constipation is due to one of three broad causes: colonic inertia, obstructed defecation, or both. The history is the first clue to what is causing the constipation. If a patient has colonic inertia, the colonic transit of stool is delayed; the stool never reaches the rectum, and the patient feels increasingly bloated and miserable. They rarely get an urge to pass stool. If a patient has outlet obstruction, the stool reaches the rectum, so the patient feels an urge to defecate, but they have great difficulty passing it, sitting for a long time on the toilet, trying to get it out. If the patient has had outlet obstruction for some years, the colonic peristalsis can become weaker and weaker until the patient has a combination of colonic inertia and obstructed defecation. The management of severe colonic inertia includes colectomy, with ileorectal anastomosis or ileostomy. The management of outlet obstruction depends on the cause of the obstruction. This week’s question addresses the differential diagnosis of outlet obstruction defecation.