Introduction: Hormones including cortisol, testosterone, estrogen and progesterone may play a role in the pathophysiology of suicide. Testosterone is a steroid hormone from the androgen group. The best known neurobehavioral effects of testosterone are on sexual function and aggression. Considerable evidence suggests that testosterone may be involved in the neurobiology of mood disorders and suicidal behavior. Methods: A review of the relevant literature including own publications in this field. Results: Many studies suggest that testosterone plays a role in the regulation of mood and behavior. Most but not all investigations of the relationship between testosterone and suicidality in men found relations between testosterone and suicidal behavior. A link between testosterone and the pathophysiology of suicidal behavior may be related to: a) a direct effect of testosterone on suicidality via certain brain mechanisms; and/or b) a testosterone influence on aggression and, consequently, suicidality; and/or c) a testosterone effect on mood and, consequently, suicidality; and/or d) a testosterone effect on cognition and, consequently, suicidality. Low testosterone levels may be associated with suicidal behavior in older men while high testosterone levels may be related to suicidal behavior in adolescents and young adults. The effect of high testosterone levels on suicidality in adolescents and young adults may be mediated by testosterone-related elevated aggression. In older men, decreased testosterone levels are associated with depressive symptoms and reduced cognitive function. Depression and reduced cognition are associated with suicidal behavior and may mediate the effect of decreased testosterone levels on suicidality. It has been recently suggested that androgen effects play a role in the transition from suicidal ideation to suicide completion. Both an increased prenatal androgen load (with subsequent permanent neuroadaptations) and increased adult androgen activity are involved in suicide completion. Testosterone may play a role in the pathophysiology of suicidality in women. Our study has shown that higher baseline testosterone levels predicted suicide attempts during the follow-up period in women with bipolar disorder. Conclusion: The balance of evidence is in favor of the view that testosterone is involved in the neurobiology of suicidality. Further studies of the role of testosterone in the pathophysiology of suicidal behavior and psychiatric disorders associated with elevated suicide risk are merited.