The neuropeptide oxytocin (OT) has a solid reputation as a facilitator of social interactions such as parental and pair bonding, trust, and empathy. The many results supporting a pro-social role of OT have generated the hypothesis that impairments in the endogenous OT system may lead to antisocial behavior, most notably social withdrawal or pathological aggression. If this is indeed the case, administration of exogenous OT could be the "serenic" treatment that psychiatrists have for decades been searching for.In the present review, we list and discuss the evidence for an endogenous "hypo-oxytocinergic state" underlying aggressive and antisocial behavior, derived from both animal and human studies. We furthermore examine the reported effects of synthetic OT administration on aggression in rodents and humans.Although the scientific findings listed in this review support, in broad lines, the link between a down-regulated or impaired OT system activity and increased aggression, the anti-aggressive effects of synthetic OT are less straightforward and require further research. The rather complex picture that emerges adds to the ongoing debate questioning the unidirectional pro-social role of OT, as well as the strength of the effects of intranasal OT administration in humans.