A 37-year-old woman with severe atopic dermatitis, was commenced on mycophenolate mofetil (MMF). Over the preceding 5 years she had been managed in our unit and treated with phototherapy, ciclosporin and azathioprine. MMF was started at an initial dose of 500 mg daily, and increased to 1 g twice daily with good clinical effect. However, 18 months into this treatment, the patient was noted to be short of breath with a dry cough and pleuritic chest pain. Serum autoimmune screen, hepatitis and human immunodeficiency virus serology were unremarkable, as were routine haematology and biochemistry. Serum IgA was slightly elevated at 3.8 g/L (normal range 0.6-3.10 g/L) but IgG and IgM were within the normal range.The patient was treated with oral amoxicillin 1 g three times daily and clarithromycin 500 mg twice daily.High-resolution computed tomography (CT) of the chest revealed bilateral ground-glass opacification, consistent with interstitial lung disease (Fig. 1). CT-pulmonary angiography demonstrated no evidence of pulmonary embolism.The patient was too hypoxic to undergo bronchoscopy. A lung biopsy was therefore taken using video-assisted thoracoscopic surgery. Histological examination revealed diffuse homogeneous expansion of the interstitium, with an infiltrate of lymphocytes and histiocytes. No granulomas or viral inclusion bodies were seen, and stains for acid-fast bacilli and Pneumocystis jirovecii were negative. Tissue culture from the specimen was negative, as were blood culture and serum precipitins. Owing to a dry cough, sputum was unobtainable, despite physiotherapy. Figure 1 High-resolution computed tomography of the chest demonstrating ground-glass opacification, consistent with interstitial lung disease. ª 2016 British Association of Dermatologists 702 Clinical and Experimental Dermatology (2016) 41, pp702-703 C P D A memorable patient T. J. Tull, T.