Motility disturbances of the colon can give significant symptoms in patients with diabetes mellitus. Constipation is a common complaint in these patients. Diarrhea associated with a generalized autonomic neuropathy can be very troublesome. There is a disturbance in the gastrocolonic response to eating in patients with diabetes mellitus who have constipation. These patients have no postprandial increase in colonic motility. However, their colonic smooth muscle contracts normally to the exogenous administration of neostigmine or metoclopramide. Stool softeners used in combination with the smooth muscle stimulants (neostigmine or metoclopramide) are helpful in treating constipation in patients with diabetes mellitus. Diarrhea can be treated with loperamide or diphenoxylate. Biofeedback may be useful in treating incontinence associated with diarrhea in these patients.