Masculinisation and adult fertility in the male are dependent on appropriate fetal endocrine programming. There is also now increasing evidence to indicate that the same mechanisms which regulate masculinisation also affect the general wellbeing of males throughout their life and, particularly, during ageing. Testosterone, secreted by the fetal testes, is the main factor regulating these processes and an understanding of fetal testis development in the human male is essential if we are to prevent adult reproductive disorders. This review focuses on what is known about human testis development and describes the effects of maternal smoking, a surrogate of possible xenotoxicant exposure on fetal testis and fetal liver function.