Vitamin D (VitD) has been found to have many effects on systems in the body; these include the immune, cardiovascular and muscular system. In the elderly vitamin D (VitD) deficiency is implicated in reduced skeletal muscle function and physical performance (PP); however very few studies have been done to look at the effects of vitamin D deficiency on athletics performance in collegiate and recreational athletes. The purpose of this study was to (1) Determine the prevalence of vitamin D insufficiency and deficiency among Collegiate Athletes and athletic persons from the general public, (2) Determine if a 12-week VitD supplementation at 28,000IU/week in VitD insufficient or deficient athletes raises Vit D levels to a sufficient range, and (3) Determine VitD supplementation of 28,000IU/week improves physical performance in Vit D insufficient or deficient athletes. Methods: 93 athletes completed baseline measurements of serum calcidiol 25(OH)D levels, height, weight, body composition, a Block calcium/VitD questionnaire and a sun log. Athletes with serum calcidiol below 30ng/mL performed 5 PP tests (30m sprint, standing long jump, vertical jump, leg strength and flexibility) and were randomly assigned to a placebo control or VitD supplement (28,000 IU of VitD/week) group for 16 weeks. Post-intervention measures were the same as those collected at baseline. Results 30.1% of the subject populations were VitD deficient or insufficient at baseline while 69% of the populations were sufficient. Of the VitD insufficient or deficient athletes, 75% were African-American. Serum levels of VitD supplemented subject were raised to sufficient levels (39.3±5.1 ng/mL). There was no significant difference in any performance variable from pre to post intervention; however there were significant positive correlations between serum 25(OH)D and flexibility (r=0.55, p=0.03), serum 25(OH)D and type II fiber percentage (r=0.66, p=0.005) and sun exposure and leg strength (r=-0.51, p=0.04). Conclusion: VitD deficiency and insufficiency is highest among African American athletes and VitD supplementation at 28,000 IU / week will raise serum levels to significant levels, but was ineffective in increasing athletic performance.