Pulmonary complications of ulcerative colitis (UC) are relatively rare. Generally, pulmonary lesions with cavity formation are difficult to distinguish from infections or Wegener's granulomatosis lesions. A 15-year-old female with no remarkable past medical history had multiple pulmonary nodules on chest X-ray. Since empirical treatment with wide-spectrum antibiotics did not improve her symptoms, she was transferred for further evaluation. Chest radiography and computed tomography (CT) scan showed multiple bilateral pulmonary nodules with cavity formation, 8-65 mm in diameter, located mainly in the right lung. She was diagnosed with UC based on sigmoidoscopy. She was treated with mesalazine and granulocyte-monocyte apheresis (GMA). Steroids were not administered, because an infectious disease could not be excluded. Seven days after starting GMA, her symptoms and laboratory findings improved, and she was discharged. After the completion of 10 courses of GMA, chest radiography and CT scan showed marked diminution of the pulmonary lesions. UC-associated pulmonary lesions can be treated without steroid administration, and we suggest that this strategy is an option for a patient with UC-associated pulmonary lesions that cannot be differentiated from an infection.