We report a 34-year-old woman with psoriasis who developed shortness of breath during methotrexate therapy. Methotrexate had been started 4 months earlier and the patient had ingested a cumulative dose of 232 mg. Pulmonary function tests showed a reduction in transfer factor to 76% of predicted. Methotrexate was stopped and her symptoms rapidly resolved. Pulmonary function tests deteriorated further despite stopping methotrexate but with no recurrence of symptoms with a transfer factor of 66% of predicted 2 months later. At 5 months after stopping methotrexate the patient remained well and pulmonary function had improved with a transfer factor of 79% of predicted. Pulmonary toxicity is a rare but important adverse effect of methotrexate therapy in patients with psoriasis.