In order to explore the high-resolution CT (HRCT) findings of cytomegalovirus (CMV) pneumonitis after bone marrow transplantation, we retrospectively reviewed the HRCT findings in nine patients with CMV pneumonitis cytologically proven by bronchoalveolar lavege. In 67% of cases, HRCT showed ground-glass attenuation. Consolidation and bronchial wall thickening were demonstrated in 33%, pleural effusion in 22%, and micro centrilobular nodules, bronchiectasis, and reticulation in 11%, respectively. Lymphadenopathy and masses were not seen. The areas of ground-glass attenuation were distributed bilaterally in all cases, diffusely in 67%, centrilobularly in 50%, and panlobularly in 50%. Subpleural lung regions were spared in 83%. The areas of consolidation were bilateral in 67%, nonsegmental in 67%, and involved the lower lobe in all cases. A total of 25 follow-up HRCT were performed in six patients. Small centrilobular ground-glass opacities disappeared after treatment in one patient. Micro centrilobular nodules vanished after treatment in one patient. Small centrilobular ground-glass opacities developed into consolidation and resolved after treatment in one patient. In one patient, diffuse ground-glass opacities progressed to consolidation, and the patient died due to respiratory failure. No abnormal findings were observed in two patients. It may be considered that in the early phase of CMV pneumonitis HRCT shows small or micro centrilobular ground-glass opacities and nodules and that in the advanced phase these lesions progress to dense alveolar opacities as CMV infection advances, although a variety of HRCT appearances is observed in the course of CMV pneumonitis.