Sevelamer carbonate is an anion-exchange, nonabsorbable resin that is commonly used to treat hyperphosphatemia in patients with advanced chronic kidney disease and end-stage renal disease. It is generally well-tolerated with only mild gastrointestinal symptoms such as abdominal pain, nausea, vomiting, and constipation. There have been few case reports of gastrointestinal mucosal injury resulting from sevelamer crystal deposition. The severity of presentation varies from acute inflammation to polyp formation, necrosis, ulceration, and intestinal perforation. We report a 77-year-old woman with end-stage renal disease who was found to have mucosal injury from sevelamer crystal deposition resulting in colitis and ulceration.