Geneticists have a long history of studying reproduction in the fruitfly, Drosophila melanogaster, and in recent years it has become apparent that many of the genes that regulate invertebrate reproduction have been conserved through vertebrate evolution. As with other higher eukaryotes, spermatogenesis in Drosophila is characterized by a regenerative germline stem cell population that divides asymmetrically to produce mitotic spermatogonia which will eventually differentiate into spermatocytes. Germline tumours consisting of undifferentiated germ cells have been associated with both loss-of-function mutations and ectopic gene expression. While the genesis of these tumours may not be identical to human germ cell tumours many of the genes that regulate stem cell proliferation and aberrant over-proliferation in the Drosophila testis provide candidate molecules that may underlie the genetic programmes that contribute to human testicular oncogenesis.