Cranial imaging studies (radiographs, computed tomographic [CT] scans, magnetic resonance [MR] images, and bone marrow scintigrams) in 13 infants and children with autosomally recessive osteopetrosis were reviewed to characterize patterns of facial and calvarial involvement at presentation and with progression of disease. In the mandible, a characteristic triangular opacity representing calcification within the secondary condylar cartilage ossification center was seen in 10 of the 13 patients. Defective dentition with incomplete enamel formation and/or caries was encountered in all patients. The paranasal sinuses were poorly pneumatized in all patients, but the ethmoid sinuses tended to be the least severely affected. Hypertelorism was present in five of the 13 patients, with a characteristic "space-alien" appearance on frontal radiographs. In younger patients, the calvarium demonstrated a high-attenuation inner table, a broad, low-attenuation diploic space, and a less high-attenuation outer table at CT. In three older children, a "hair-on-end" appearance was seen, which, at bone marrow scintigraphy, corresponded to areas of marked hematopoietic activity. Regions of sclerotic bone demonstrated low signal intensity on both T1- and T2-weighted MR images; areas containing marrow had intermediate signal intensity. These many new radiologic features of osteopetrosis are related to its pathophysiologic characteristics.