Accumulation of visceral adipose tissue is an independent marker for cardiovascular risk and insulin resistance in both children and adults (Gower et al, 1999; Neeland et al. 2012; Owens et al. 1998). As the accumulation of visceral adipose tissue increases the risk of cardiovascular also increases independently of total obesity (Nakamura et al. 1993). Given its location surrounding the visceral organs, accurate measurement of visceral adipose tissue presents a challenge. The first reliable methods for quantifying visceral adipose tissue were computed tomography and magnetic resonance imaging. These procedures, while valid and reliable, are associated with several limitations and generally rely on a single slice to estimate visceral adipose tissue. Recently, dual energy x-ray absorptiometry (DXA) has been validated against computed tomography as a valid and reliable estimate of visceral adipose tissue (Kaul et al. 2012) and a significant marker of cardiometabolic risk in adults (Katzmarzyk, et al. 2013; Rothney et al. 2013). This dissertation will investigate the use of this novel method in three distinct populations: children; adults; and professional football players. We hypothesize that DXA will provide a valid estimate of visceral adipose tissue in children and be associated with cardiometabolic risk factors. Secondly, we hypothesize that differences in regional body composition exist in professional football players. Finally, we hypothesize that a threshold exists in distribution of fat to the visceral region and that this threshold is associated with increased cardiometabolic risk. The results of this dissertation will provide further insight into the reliability and clinical utility of DXA for estimating visceral adipose tissue.