We studied eight affected and four unaffected individuals from a Colombian family with autosomal dominant diffuse high bone density. Affected individuals have normal, proportional height and high serum alkaline phosphatase activity. Radiographically, affected members exhibit generalized, symmetrically diffuse endosteal hyperostosis of the long bones and skull with narrow medullary cavities and loss of the diploë, respectively. There is no periosteal reaction or decreased hematopoiesis. Furthermore, osteosclerosis affects vertebral bodies, ribs, pelvis, mandible, clavicles, and scapulae. Bone mineral density is 2.4-7.3 SD above the mean for age and gender in affected individuals. Affected vs. unaffected individuals' Z-scores were (mean +/- SD) 5.03 +/- 1.77 vs. 0.08 +/- 0.97, respectively, P = 0.0004). Three affected subjects older than 40 yr old lost bone mass in 6 yr. No dysmorphism, abnormal facial features, bone fractures, or cranial nerve involvement was found. The pattern of inheritance, the absence of asymmetries and malformations, the increased serum alkaline phosphatase, the peak bone mass that appears to decrease physiologically with age, and the involvement of cortical and trabecular bone suggest a new variant of hyperostosis/osteosclerosis that affects the entire skeleton.