Pulmonary alveolar microlithiasis is a rare pulmonary disorder of unknown etiology characterized by intra-alveolar development and deposition of microliths or calcispherytes consisting of calcium phosphate. Approximately 400 cases of this rare disorder have been described in the literature. The age range of patients is from newborn to 80 years, with a mean age at diagnosis of about 35 years. No sexual predominance has been noted. In about half of the reported cases, a familial pattern has been found, with the disease usually affecting the siblings. The progression of the disease is generally very slow, some patients having been followed up for more than 30 years without evidence of change. Pulmonary function studies demonstrate a tendency toward a restrictive pattern. Chest roentgenography, high-resolution computed tomographic chest scan, and technetium-99m lung scan are useful in the diagnosis. A definitive diagnosis can be established by bronchoalveolar lavage or lung biopsy. There is no known therapy for this unusual disorder. In patients who develop progressive respiratory insufficiency and cor pulmonale, lung transplantations have been performed.