It is 25 years since the discovery of the testis determining factor, SRY. Its biological function in male sex determination and testis development during embryogenesis is pretty clear, steering cell and gonadal fate down the male pathway and actively away from the female pathway. However, we still don't know its precise molecular functions. Clues have emerged through studies of patients with disorders of sex development, so-called 'XY females', who carry missense mutations in SRY. SRY is a nuclear protein, that binds and bends DNA leading to the transcriptional activation of SOX9, a 'hub' gene of sex determination among vertebrates. How this happens in vivo is partly understood. More recent roles for SRY in the most important sexual organ in males, the brain, are beginning to emerge. SRY has roles in specific brain regions such as in the control of voluntary movement, through the transcriptional regulation of genes required for catecholamine synthesis and metabolism. That SRY is a male gene for the male brain, might have implications for neurological conditions affecting males more frequently and severely, such as Parkinson's disease, ADHD and schizophrenia.