Oral mesalazine, or 5-aminosalicylate, is one of the first-choice medications for the treatment of ulcerative colitis and is commonly used for both induction and maintenance therapy. In a 6-month period, we treated three cases of mesalazine-induced pneumonitis. In all three cases, computed tomography images revealed upper lobe dominant bilateral peripherally localized consolidations. Such images are commonly observed in patients with cryptogenic organizing pneumonia or chronic eosinophilic pneumonia. Computed tomography images for mesalazine-induced pneumonitis have been rarely reported in the literature.