Pulmonary involvement with multiple myeloma occurs infrequently and may be difficult to distinguish from more common primary lung tumours, metastatic disease, or other pleural and parenchymal abnormalities. A patient who developed acute respiratory distress syndrome (ARDS) was subsequently found to have multiple myeloma with involvement of lung parenchyma by neoplastic plasma cells. Only one other report of ARDS in association with multiple myeloma was found, and there are no previous reports where the appearance of ARDS antedated a diagnosis of multiple myeloma. In patients with ARDS, parenchymal involvement from multiple myeloma should be included in the differential diagnosis.A 65 year old woman was admitted to hospital complaining of dull pleuritic retrosternal chest pain of 5 days' duration. It had been somewhat relieved with non-steroidal anti-inflammatory drugs. She also complained of a cough and worsening dyspnoea upon exertion. A 2 month history of nausea was accompanied by a weight loss of 11 lb. Past medical history included non-insulin dependent diabetes, hypertension, asthma, and obesity.On physical examination the patient initially appeared comfortable at rest but was dyspnoeic with limited activity. Her temperature was 101.7˚F, heart rate 96 beats/min, respiratory rate 20 breaths/min, blood pressure 117/ 72 mm Hg. The only significant physical finding was bilateral basilar crackles. Laboratory data revealed a white blood cell count of 10 400/mm 3 and haemoglobin of 9.7 g/dl. The serum sodium was 131 mEq/l, total calcium 8.5 mg/dl, and creatinine 1.0 mg/dl. Urinalysis revealed trace protein. The chest radiograph showed bilateral multifocal areas of nodular consolidation (fig 1), and the ECG showed normal sinus rhythm with diffuse non-specific T wave abnormalities. Serum troponin levels were normal. Oxygen saturation was 88% on room air and 94% on 5 l oxygen via nasal cannulae.The patient's respiratory status steadily declined over the ensuing days, despite treatment with antibiotics for presumed pneumonia. Four days after admission she was in acute respiratory distress with tachypnoea and the use of accessory muscles. Arterial blood gas showed pH 7.46, PaCO 2 5.2 kPa, and PaO 2 4.5 kPa on 50% FiO 2 non-rebreather mask. She required intubation and mechanical ventilation with a low tidal volume high positive end expiratory pressure protocol. Bronchoalveolar lavage yielded fluid that contained 40% macrophages, 25% neutrophils, and 35% lymphocytes. No malignant cells and no pathogens were identified. All blood, sputum, and urine cultures were negative. A chest CT scan showed diffuse, patchy, multifocal air space consolidation bilaterally with a nodular character, small bilateral pleural effusions, mediastinal lymphadenopathy, and a questionable lytic lesion of the T9 vertebra.