We aimed to compare gastrointestinal transit and defecatory function in a random sample of people with or without diabetes mellitus in a US community who reported constipation or laxative use. In this pilot study we measured: gastric, small bowel, and colonic transit by scintigraphy; vector manometry of anal sphincters at rest and during squeeze; defecatory dynamics by balloon expulsion test; and scintigraphic measurement of anorectal angle at rest and during defecation. Autonomic function tests were performed in diabetics. Diabetics with constipation had a higher prevalence of abnormal evacuation or prolonged colonic transit during the first 24 hr than controls (P = 0.07): three had prolonged 24-hr colonic transit, and three abnormal evacuation. Among constipated controls, only one had anismus. Overall, diabetics had slower colonic transit during the first 24 hr than nondiabetics (P < 0.05). Community diabetics who experience constipation or use laxatives have a greater prevalence of delayed 24-hr colonic transit or evacuatory dysfunction than community controls.