Sulfasalazine is a compound of 5-aminosalicylic acid and sulfapyridine joined by an azo bond. There are only case reports in the literature about pulmonary toxicity caused by this drug. A 23-year old man diagnosed as ulcerative colitis 3 months ago admitted to our hospital with a 1 month history of fever, cough, dyspnoea. He didn't respond to antibiotics. He was a nonsmoker and had been on sulfazalazine and mesalazine treatment for 8 weeks. All of his medications were held on admission. He had fever (38.6 °C) with respiratory rate of 20/min with normal oxygen saturations in room air Physical examination revealed crepitation over right lung on auscultation. Chest radiograph showed multilobar pulmonary infiltrates dominated right lung peripherally . He has peripheral eosinophilia. For differential diagnosis, an autoimmune screen, Ig E level and parasite search in his feces was negative. Sputum culture was negative for pathogenic bacteria and acid-fast bacilli. HRCT revealed patchy consolidations at all zones of the right lung and upper zone of left lung, peribronchial and interlobuler septal thickenings, ground glass opasities. No endobronchial pathology was detected. Bronchoalveolar lavage done from medial segment of right middle lobe was negative for viral, tuberculous and fungal infections. The differential cell count showed 20% eosinophils. After withdrawal of sulfazalazine, pulmonary infiltrates started to regress in the control chest radiograph but respiratory symptoms were not resolved completely so oral prednisone treatment was started. 2 weeks later, his chest radiograph was dramatically improved with near complete resolution of the pulmonary infiltrates.The patient is in our follow up for 6 months without any symptoms.