Two hundred sixty patients with severe chronic constipation were studied by rectal biopsy, barium enema, and anorectal manometry. None had any medical, neurologic, or anatomic cause for their complaint. All biopsies showed presence of ganglion cells and absence of hypertrophied nerves. Barium enemas showed a dilated anorectum (otherwise normal colon) in 183 (70%) and a normal anorectum and colon in 77 (30%). Manometry showed three patterns. One hundred seventy-eight patients (68%) had pressures between 0 and 20 mmHg with normal anorectal reflex, 69 (26%) had pressures between 0 and 20 mmHg with absence of anorectal reflex, and 13 (16%) had high pressures (20 to 60 mmHg) with normal anorectal reflex. One hundred seventy-eight patients (68%) were treated conservatively by diet and/or laxatives and did well. Eighty-two (32%) required a posterior internal sphincter myectomy after failure of prolonged conservative therapy. All patients were given senna postoperatively (one tablet or one teaspoon every night). Thirty-five patients (43%) did not require the senna after a few months and have daily bowel movements. Forty-two patients (51%) are still using senna. Ten (12%) experienced occasional impaction relieved by enemas. Two recurrences required reoperation. Five (6%) did not benefit from the operation. Sixteen had immunoperoxidase antineurofilament studies that showed no distinctive pattern as described by Kluck et al.