Cytomegalovirus (CMV) pneumonia is one of the most common pulmonary complications after bone marrow transplantation (BMT). We describe the high resolution CT (HRCT) findings of 13 patients with CMV pneumonia diagnosed after allogenic BMT. The study included 13 consecutive patients who developed CMV pneumonia after BMT and who had HRCT of the chest performed within 24 h of the onset of symptoms. HRCT scans were reviewed by two radiologists who assessed pattern and distribution of findings. There were nine male and four female patients, ranging from 9 years to 56 years of age (mean age 33 years). BMT was performed for treatment of chronic myelogenous leukaemia (54%), severe aplastic anaemia (23%), acute myelogenous leukaemia (15%) and Fanconi's anaemia (8%). The time elapsed until diagnosis ranged from +18 days to +405 days (median of 54 days, mean +81.6 days). The predominant patterns of abnormality on HRCT scans were ground-glass opacities (69%), small centrilobular nodules (69%) and air-space opacities (54%). The abnormalities were distributed in the central and peripheral zones of the lungs in six cases, only in the periphery in four cases, and only in the central zone in three cases. In all cases the lung lesions were bilateral, and asymmetry was observed in seven cases. The authors conclude that the most common HRCT findings in patients with CMV pneumonia after BMT consist of bilateral asymmetric ground-glass, air-space opacities and small centrilobular nodules.