Sex specific behaviors are essential for the reproductive success of individuals and the propagation of the species. Gonadal steroid hormones are critical regulators of reproductive behaviors, yet the neural regulation of these behaviors at the molecular level remains largely unknown. We hypothesize that the genes that regulate such behaviors are expressed in a sex specific fashion in the brain and are regulated by steroid hormones. Using both microarray and in situ hybridization screening of adult male and female mouse brains, we have identified sixteen genes with sex specific expression in the hypothalamus and the amygdala. This sex specific expression is regulated by adult hormones, demonstrating that the identified genes are downstream targets of gonadal hormone signaling. We find that five of these genes are required for proper expression of components of sex specific behaviors in mice. The link between these novel sexually dimorphic genes and the regulation of sex specific behaviors provides new insights into the molecular and neural mechanisms that regulate reproductive behaviors.