PURPOSE: To assess the differences in bone mineral density (BMD) of lumbar spine and wrist between preterm infants of postconceptional age 40 weeks and normal full-term infants. MATERIALS AND METHODS: Sixty-eight preterm infants born at conceptional age 26 -36 weeks and 31 normal full-term infants born at 38 -42 weeks were investigated. Bone mineral densities of the lumbar spine (from the second to the fourth segment) and wrist were measured by dual energy X-ray absorptiometry. In preterm infants, the corrected age of 0 month was defined as postconceptional 40 weeks. Full-term infants were evaluated within three days of birth, and the average bone mineral densities of preterm and full-term infants were compared. In the preterm group, birth weight and conceptional age were correlated with lumbar spinal and wrist bone mineral densities. Data were analyzed by student's t-test and Pearson's correlation coefficient, and a pvalue of less than 0.05 was considered significant. RESULTS: In preterm in fants, the values of bone mineral densities of the lumbar spine and wrist were 0.137 +/- 0.018 g/cm2(0.061 -0.202 g/cm2) and 0.089 +/-0.013 g/cm2 (0.065 -0.123 g/cm2), respectively, while the respective values for full-term infants were 0.214 +/-0.030 g/cm2 (0.160 -0.296 g/cm2) and 0.118 +/-0.014 g/cm2(0.096 -0.162 g/cm 2). In the preterm group, lumbar spinal BMD correlated significantly with conceptional age(r=0.384, p<0.05) and birth weight (r=0.438, p<0.05). While wrist BMD correlated significantly with birth weight (r=0.281, p<0.05), its correlation with conceptional age was not significant (r=0.223, p>0.05). CONCLUSION: The lumbar spinal and wrist BMDs of preterm infants at corrected age 0 were lower than those of normal full-term infants. In the preterm group, BMD values for the lumbar spine were lower in infants of lower conceptional age and birth weight.