Osteoporosis is a disease that plagues older individuals, particularly women. At the usual age of diagnosis, limited therapy is available. By further delineating the factors that influence bone mineral acquisition before peak bone density is achieved, individuals at risk may be identified at an earlier age when therapies may be more effective. This was a study of 16 family units, 16 mothers, eight fathers, and their 28 children between the ages of 5 and 20 years. The evaluation consisted of a focused history, Tanner staging of adolescents, anthropometric data (height, weight), and spinal bone mineral density (BMD) by DEXA (dual-energy x-ray absorptiometry). Bone mineral density in the children was compared with multiple environmental factors. Bone mineral density Z-scores were then compared between children and their parents. Variables found to be positively correlated with children's BMDs were: age (r = 0.94, P < 0.001), Tanner stage (r = 0.90, P < 0.001), weight (r = 0.88, P < 0.001), height (r = 0.81, P < 0.001), and body mass index (r = 0.77, P < 0.001). No association was found between calcium intake and BMD, owing possibly to increased calcium intake among children with a family history of osteoporosis. Activity was not significantly associated with BMD. Significant correlations were noted between the children's BMD and that of their father's (r = 0.83, P = 0.01), premenopausal mother's (r = 0.58, P = 0.03), and midparental (the mean value of both parents' BMDs) (r = 0.86, P = 0.01). These data suggest that children who have parents affected by low BMD may be at risk for low BMD themselves.