A young man without any past history of note had taken isotretinoin for disfiguring acne before the summer season. He presented with a severe bilateral pneumonia, associated with dyspnoea two months after the start of treatment. On the pulmonary radiography there was a bilateral ground glass appearance which was worse on the right. The elevated level of eosinophils (54% in 564,000 cells/ml) in the alveolar lavage lead to a diagnosis of allergic pneumonia. The rapidly favourable outcome following the cessation of the medication and with the addition of corticosteroids seemed to us a supplementary argument in favour of a diagnosis of eosinophilic pneumonia, due to isotretinoin which seemed the primary initiating factor.