Mesalamine-induced lung toxicity has often been described. We report on a case of a patient who underwent mesalamine treatment, though in the absence of established criteria required for diagnosing Crohn's disease (CD) or ulcerative colitis (UC). He developed an adverse respiratory reaction to the drug, thus definitely proving its lung damaging capacity. The clinical presentation included eosinophilic pleural effusion, a feature never previously described in association with mesalamine intake.