Hirschsprung's disease (HD) in adults is rare and often undiagnosed or misdiagnosed. We report a case of HD in a 26-year-old woman who had a history of chronic constipation that required laxatives and enemas since early childhood. She developed severe intestinal obstruction and presented to the emergency department with significant abdominal distension. A computed tomographic scan confirmed significant fecal loading of the entire colon and rectum. An anal manometry revealed lack of normal rectoanal inhibitory reflex. A rectal biopsy showed hypoganglionic anorectum, suspicious for HD. Because of the severe fecal retention that was refractory to conservative management, total proctocolectomy with ileal pouch-anal anastomosis was performed. The entire colon showed massive dilatation and marked wall thickening. Histologic examination showed absence of ganglion cells in submucosal (Meissner's) and myenteric (Auerbach's) plexuses in the distal rectum. A diagnosis of adult HD was made. Her postoperative course was uneventful with complete resolution of the symptoms. Hirschsprung's disease should be considered in adults who have long-standing and refractory constipation.