Here, we report a case of MEN2B-associated megacolon that was managed surgically, resulting in a favorable outcome.<h4>Case presentation</h4>A 23-year-old man with a history of chronic constipation was diagnosed with MEN2B at 14 years of age based on findings of medullary thyroid carcinoma, mucosal neuromas, and rectal biopsy-confirmed intestinal ganglioneuromatosis. The gene discussed is RET; the disease is medullary thyroid gland carcinoma.