Fat-free mass includes the body's water, organs, bone, and muscle content. Fat-free mass index (FFMI) is calculated as FFM/height2, and it helps indicate the body's muscle development and can help prevent injury. PURPOSE: The objective of this study was to compare measured FFMI between university club athletes within their sport. METHODS: Multicomponent (4C) model body composition using the Bod Pod to measure body volume, dual-energy x-ray absorptiometry (DXA) to measure bone mineral content, and bioimpedance spectroscopy (BIS) to measure total body water was used. Multicomponent methods: evaluation of new and traditional soft tissue mineral models by in vivo neutron activation analysis. RESULTS: Data from 118 club sport athletes (45 female, 73 male) revealed a statistically significant difference (p<.001) between men's and women's FFMI. Men (21.2 +/- 2.0 kg/m2) had a significantly greater FFMI (p < .001) compared to women (17.9 +/- 1.7 kg/m2). For sports with more than 1 participant tested, women's lacrosse had the lowest FFMI (16.7 +/- 1.0 kg/m2) and powerlifting had the greatest FFMI (20.3 +/- 0.2 kg/m2). For both men and women, the difference in FFMI was significant across sports (p = .001). CONCLUSION: FFMI values generally fell in the same range for athletes within each sport. This can be used to form a database of average FFMI values for university club sports athletes."