Abstract Introduction – In 1991, during a biological follow up, we found a testis cancer on a top level swimmer. Synthesis of facts – This testis cancer was without significant clinic expression. Biological control was abnormal. Accurate blood tests found an increase of plasmatic βHCG and then of αfoeto protein. The testis echography showed a possible tumor of left testis. Orchidectomy was realized with histo-pathologic examination. The diagnosis of germ cell carcinoma was found. Chemotherapy used a regimen with VP16 and cisplatin. The subject performed 6 months later the diagnosis at the National Swimming French Championship. In 2000, the subject is one of the best French specialist of free water long distance swimming. Conclusion – Testicular cancer is frequent in young men. Modern chemotherapy modifies the prognosis. Early diagnosis is preponderant for an efficient therapy. In our observation, the patient hasn't received any corticotherapy or hematopoietic growth factors. After curing, the come back to the best level has been obtained with a sport training in a lawful and ethical medical assistance.