Alimentary tract manifestations were found in all of 17 patients with multiple endocrine neoplasia, type 2b. The manifestations are important because (1) they were chronic, (2) they were severe and led to abdominal operation in 5 patients, (3) they antedated detection of the endocrine neoplasms in the syndrome in 16 patients (94%), and (4) they provided clinical clues that stimulated search for thyroidal C-cell and adrenal medullary disease in 6 patients. The alimentary tract manifestations were diverse: symptoms included constipation, diarrhea, difficulty with feeding, projectile vomiting, crampy abdominal pain, and loud borborygmi; findings included thickened lips, nodules on the anterior third of the tongue, abdominal distention, visible peristaltic waves, and roentgenographic evidence of megacolon or diverticulosis of the colon or of dilatation of the small intestine and stomach. Initial misinterpretation or failure to realize the significance of one or more of these alimentary tract manifestations led to suspicion of aganglionic megacolon (three patients), malabsorption syndrome (two patients), and tracheal ring (one patient).