Sevelamer carbonate is a commonly prescribed anion-exchange resin administered orally to prevent hyperphosphatemia in patients with chronic kidney disease. We present a rare case of a 33-year-old man with end-stage renal disease and diabetic gastroparesis on sevelamer carbonate, who presented with hematochezia and was found to have rectosigmoid ulcers induced by sevelamer crystals. His hematochezia resolved after switching from sevelamer carbonate to lanthanum carbonate. Clinicians and pathologists must be aware of the possibility of drug-induced mucosal ulceration associated with sevelamer use as a potential etiology of a gastrointestinal bleed.