Although the side effects of thalidomide are well known, lung toxicity has not been reported. We describe the case of a 65-year-old man with multiple myeloma (IgG kappa) in stage IA who, on the thirty-seventh day of treatment with thalidomide, developed acute coughing, general malaise, dyspnea at rest and sudoresis. Blood pressure was 90/60 mm Hg and temperature was normal. An interstitial and alveolar pattern was visible on the right side of a chest film and arterial blood gases indicated partial respiratory insufficiency (pH 7.40, PaCO2 40 mmHg, PaO2 47 mmHg). Blood analysis showed alterations expected for multiple myeloma and microbiology was negative (sputum and blood cultures and urinary antigen detection for Streptococcus pneumoniae and Legionella pneumophila). After thalidomide was withdrawn and oxygen and intravenous corticoids were administered, outcome was good. A chest film 4 days later was normal and arterial blood gases showed that respiratory insufficiency had disappeared. We conclude that severe lung toxicity should be included among the potential adverse effects of thalidomide.