Testosterone has important effects on brain structure development and function during fetal, neonatal, and pubertal development that result in increased brain volumes in specific locations that include the prefrontal cortex, amygdala, and hippocampus—structures that are important for modulating behavior. The importance of these androgenic effects on differentiation between male-typical and female-typical behavior including aggression and violence remains unclear. The current evidence indicates that serum testosterone concentrations that are typical for healthy men are important for maintaining mood, but testosterone therapy is generally not helpful for treatment of persistent depressive symptoms in men with mild to moderate hypogonadism.