Objectives. To identify supplement use among patients diagnosed with testicular cancer. The incidence of testicular cancer has increased, as has supplement use, including those designed specifically for exercise performance enhancement. Methods. A questionnaire was administered to patients with testicular germ cell cancer treated at our institution between 1990 and 2004. This survey addressed the use of supplements before, during, and after the diagnosis of cancer. Results. Of the 129 patients who completed the questionnaire, 26 (20.1%) used some form of supplements, most of which were ingested for exercise performance enhancement. The most common supplement taken was protein/amino acids (12.4%) followed by creatine (9.3%) and androstenedione (1.6%). The mean duration of supplement use was 17.0 months. The mean age of the patients who had used supplements was 27.6 years (median 26, range 17 to 47) compared with 35.7 years (median 34, range 14 to 76) for patients who had not used supplements. Of the 57 patients diagnosed before 2000, 9 (16%) reported supplement use and 3 (5%) reported creatine use. Of the 72 patients diagnosed during or after 2000, 17 (24%) reported supplement use and 9 (13%) reported creatine use. Conclusions. Supplement use is common and increasing among patients with testicular cancer. The use of exercise performance-enhancing supplements was as great as 20%. Given the increasing incidence of testicular cancer, coupled with the widespread use of these performance-enhancing supplements in this at-risk group, additional study is required to determine what association, if any, exists between the use of these substances and the development of testicular cancer.