Report of two new pediatric cases of pulmonary alveolar microlithiasis (PAM). PAM is a rare disease of unknown etiology; not more than 38 cases have been reported aged less than 18 years. The essential features of this disease are (1) a characteristic radiographic appearance of a sand-like opacity of both lungs and linear densities like "beads on a string" along the heart, pleura and interlobar fissures; this is best visualized by fluoroscopy in combination with magnification technique; (2) extremely few clinical signs and almost no laboratory abnormalities.