Large intestinal, descending colon, distal colon transit times were delayed in diabetics with autonomic neuropathy compared to non-diabetic controls and to diabetic without autonomic neuropathy (P<0.05). There was no difference in proximal colon transit times among them. There was no relationship between colonic transit and peripheral neuropathy in any of the studied subjects. Consequently autonomic neuropathy may play a more important role in gastrointestinal motility disorders rather than peripheral neuropathy. While, in diabetics with nephropathy and retinopathy, large intestinal transit times were significantly delayed. In this respect, and based on the result we reported here, we would suggest that there is a relationship between large intestinal motility disorders and microangiopathy in diabetes mellitus and that autonomic neuropathy plays a causative role in the pathogenesis of large intestinal motility disorders.