The peak incidence of testicular cancer in young men suggests that gestational development and events during early infancy and puberty are important in the pathogenesis of the disease. There are two potentially significant events: the transformation of fetal germ cells into carcinoma-in-situ cells (CIS) and later conversion of CIS cells into fully invasive cancer. Several hypotheses suggest an endocrinological background to testicular neoplasia. Based on epidemiological and experimental evidence, the possible role of oestrogens, androgens and gonadotrophins is discussed in this review. The role of Sertoli cells and the importance of interplay between endocrine and paracrine factors is also stressed.