Lung toxicity associated with 5-aminosalicylate (5-ASA) agents is very rare. We report the case of a 48-year-old man with ulcerative colitis who developed progressive shortness of breath while taking oral mesalamine. Chest imaging revealed a ground glass appearance in patchy areas distributed throughout the lung. He had a restrictive ventilatory defect with reduced diffusion capacity. He improved rapidly afterthis drug was discontinued. Mesalamine-induced lung damage must be considered in patients who develop unexplained respiratory symptoms while taking this agent.