BACKGROUND: The androgen testosterone plays a critical role in many aspects of sexual differentiation. Also, it is thought to induce aggressive behaviours or to play a role in social dominance. CASE PRESENTATION: In this case report a 4-year-old boy is described whose testosterone and dehydroepiandrosterone sulphate (DHEA-S) levels were raised to pubertal levels due to a testosterone producing testis tumour. This provided the unique opportunity to examine the effects of elevated levels of androgens on levels of aggression or on social dominance before the onset of puberty. CONCLUSION: The present case report does not support the hypothesis of a causal relationship between testosterone and aggression or between testosterone and social dominance in young children.