Bronchiolitis obliterans and organising pneumonia (BOOP) presents with fever, dyspnoea, and other features that may be mistaken for pneumonia. Treatment is, however, very different, requiring corticosteroids. A man was admitted as an emergency with fever, dyspnoea, and non-productive cough. The chest radiograph showed consolidation which, despite antibiotics, progressed to become bilateral. BOOP was considered, and confirmed by transbronchial biopsy. The response to oral prednisolone was rapid with complete resolution of symptoms and radiographic consolidation within three weeks. The cause of BOOP is often never found; it is believed, however, that in this instance it occurred as a result of carbamazepine therapy started seven weeks earlier.