In pulmonary alveolar proteinosis (PAP), a proteinaceous material accumulates in the alveolar air spaces, causing hypoxemia, restrictive lung disease, and dramatic abnormalities on chest radiographs. Complications are unusual, but of the ones that do occur, infection, particularly with Nocardia asteroides, and fibrosis are the most common. Few computed tomographic (CT) studies of this condition have been reported. The CT scans of nine patients with PAP were reviewed. Varying combinations of air-space and interstitial patterns were seen. The CT appearance of air-space disease ranged from ill-defined nodules to patchy consolidation to large regions of confluence. Air-space consolidation was sometimes sharply demarcated from surrounding normal lung tissue, which created a geographic pattern. Despite the predominance of air-space patterns, air bronchograms were not a prominent feature. CT showed the interstitial component of disease and the extent of disease more clearly than did plain radiography. In two cases, CT demonstrated focal pneumonia that was not visible on the radiographs.