Pulmonary alveolar microlithiasis (PAM) is a rare disease of unknown etiology and is characterized by the deposition of calcium phosphate microliths within the alveolar airspaces. We report 2 asymptomatic siblings, a 7-year-old girl and her 13-year-old brother, with PAM. In the girl, chest X-ray and computed tomography revealed diffuse interstitial changes but no uptake of technetium 99m (Tc-99m) on bone scan was noted in the lung. Microliths stained pink with Papanicolaou dye in bronchoalveolar ravage fluid (BALF) but did not stain with von Kossa. In the brother, characteristic radiological findings and Tc-99m uptake in the lung were detected, The microliths stained pink with Papanicolaou in BALF and black with von Kossa as well. We hypothesize that the first case is in the early phase of PAM because of lack of Tc-99m uptake. Copyright (C) 2001 S. Karger AG, Basel.