Introduction: Vitamin D deficiency is very prevalent in world population and growing evidence shows that also athletes are affected. Vitamin D deficiency causes beside bone disorders, musculoskeletal pain, muscle weakness and is associated with many other health disorders. For athletes in particular it may impair training and performance, prolong recovery and increase risk of injury. We therefore analyzed vitamin D levels in Swiss athletes focusing on prevalence according to age, gender, seasonal variations, indoor or outdoor sports, sunscreen use and vitamin D supplementation. Methods: This study was performed in a convenient sample of 655 Swiss Olympic athletes over one year.