Compared with adult athletes, rather little is known about supplementation behavior in adolescent athletes. This study’s aim was to determine elite adolescent athletes’ supplement use and sources of information relating thereto. A total of 430 (87%) of 496 questioned athletes returned the anonymized questionnaire. Thereof, 84% consumed at least one weekly supplement and 97% indicated some supplement intake during the previous 4 weeks. On average, 13.3 supplement servings were consumed per week. The 25th, 50th, and 75th percentile was 4.5, 10.5, and 20.0 servings per week, with a maximum of 67. The most prevalent supplements in use were multimineral products (41% of all athletes), multivitamins (34%), Vitamin C (34%), and Vitamin D (33%). Male athletes consumed significantly more Vitamin C and D, sports drinks, protein powder, and recovery products compared with female athletes; whereas, women consumed more iron supplements. The three most important motives for supplement use were recovery support (40%), health maintenance (39%), and performance enhancement (30%). The most frequent answers to the question “who recommended that you use supplements” were family/friends (36%), a physician (27%), and a trainer/coach (25%). The main three information sources about the supplements in use were the persons who recommended the supplementation (56%), the internet (25%), and information provided by supplement suppliers (11%). A positive doping attitude was associated with the consumption of performance enhancing supplements (p = .017). In conclusion, this study among elite adolescent Swiss athletes indicates a widespread and large-scale use of dietary supplements, which was associated with a low level of information quality.