Methotrexate, an immunomodulatory agent used for a wide variety of indications, can cause pulmonary toxicity in the form of pneumonitis, organising pneumonia, pulmonary fibrosis, pleural effusion, pulmonary infections or lymphoproliferative disease. We report a case of methotrexate pneumonitis in a patient with gestational trophoblastic neoplasia. The diagnosis of methotrexate pneumonitis is challenging, as the signs and symptoms can be caused by intercurrent infection, concomitant medications or an underlying disease condition. A high index of suspicion is required for diagnosis. Management consists of drug discontinuation and steroids in patients with respiratory failure.