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In the past, prior studies have associated adolescent idiopathic scoliosis (AIS) to abnormalities in bone mineral density (BMD) such as osteoporosis' or 'osteopenia' based on their adult definitions, but in reality very few AIS patients have clinically abnormal BMD. Fracture risk has not been correlated to Z-scores in pediatric populations, so the terms 'osteoporosis' and 'osteopenia' can not be applied to AIS. Our study examined adolescents with and without scoliosis of varying weights to better understand the relationship of BMD to body mass index (BMI). This cross-sectional retrospective study compared the dual photon X-ray absorptiometry (DXA) scans of hips and distal femora of 49 adolescents with idiopathic scoliosis and 40 normal control adolescents. Z-scores were compared using student's t-test or simple linear regression procedures to discover correlations between Z-scores and clinical and demographic variables. In both populations, there was a strong correlation with z-scores and BMI (p<.001). Scoliosis had the effect of lowering the Z-score as if the individual had 'lost' 3.4 BMI units. Essentially, thin subjects had lower BMD and heavy subjects had higher BMD. The impact of scoliosis reducing BMI scores by 3.4 units puts thin subjects in the 'low for age' level while the effect is negligible in heavier subjects. There were no subjects in either group that met the International Society of Clinical Densitometry (ICSD) definition for 'osteoporosis.''