OBJECTIVE Adult Hirschsprungs disease is a rare disease and frequently misdiagnosed as the long-standing refractory constipation. Almost all cases have short or ultra-short aganglionic segment of distal rectum. The clinical features are different from those in childhood when the diseased segment is long. Amongst the few successful operations that have been used to treat this condition, internal sphincter myectomy has been proposed as a simple and low morbidity procedure, but only a few literatures reported the results. The present study aimed to evaluate the outcomes of anorectal myectomy in adult Hirschsprung's disease. METHODS All medical records of adult Hirschsprung's disease between January 1, 1997 and April 30, 2008 were retrospectively reviewed The histological criteria for diagnosis were increase in the number of cholinergic nerve fibers in the lamina propria, muscularis mucosae, and submucosa, and the absence of ganglia in the submucosa. All cases underwent internal sphincter myectomy as the first operation. Post-operative complications, number of defecation per week, and the need for a second operation were studied. RESULTS Seven patients met the criteria. All patients had the long history of constipation. Anorectal myectomy was performed as the first operation in all cases. Four patients (57%) had good results, without complication and no further operation was needed up to the last follow-up (26-86 months). Two cases underwent subtotal and total colectomy after myectomy to achieve good results eventually. Only one patient had a poor result after Left colectomy and Total proctocolectomy with ileal pouch anal anastomosis. CONCLUSIONS Internal sphincter myectomy, the simple and complication-free procedure, provides the satisfactory outcomes for adult Hirschsprung's disease. This technique should be the first operation for this condition.