Leptin has important effects on bone metabolism. Possible relationships between leptin and bone mineral density were evaluated in the survivors of the childhood leukemia and lymphoma. Twenty patients were included the study. Anthropometric parameters, growth hormone response to provocative test, serum calcium, phosphorus, alkaline phosphates, osteocalcin, leptin levels, urinary calcium and deoxyypyridinoline levels, and bone mineral density were obtained. Anthropometric Parameters of patients were not significantly different from those of a control group. Growth hormone provocative test was abnormal in 3 patients who received cranial radiotherapy. The osteocalcin levels and bone mineral density of patients were significantly lower than in the control group (p=.001, p=.02). Nine patients were in the osteopenic and 7 were in the osteoporotic range. The leptin levels of patients were significantly lower (p=.01) than in the control group. Bone mineral density (BMD) was significantly correlated with leptin level, age, body mass index, and Tanner stage in simple correlation analysis. However in multivariate analysis only age was significant (p<.000, r:.752). Markers of bone metabolism, BMD, and leptin levels were not related with the growth hormone status of patients and did not present a con-elation with the cumulative doses of drugs. There are a few studies evaluating the relationship between BMD and leptin levels in childhood cancer. Although this study did not find any correlation between the leptin level and BMD, detailed studies of larger numbers of patients are necessary to evaluate causes of decreased leptin level and the possible role of leptin on osteopenia observed in survivors of childhood cancer.