Niels Jørgensen is specialist in medical endocrinology and certified as andrologist by European Academy of Andrology. He is head of the clinical andrology section at Department of Growth and Reproduction at Rigshospitalet in Denmark. Since 1996 Niels Jørgensen has undertaken and coordinated Danish and international scientific projects focusing on the testicular function of more than 12,000 men from the general populations, selected fertile or infertile men. Besides describing the actual testicular function (semen quality and endocrine function) these studies have also focused on addressing the impact of exogenous exposures, life style and genetic factors on testicular function and testicular function and general health.