Impulsive aggression is a key feature of a number of psychiatric disorders including schizophrenia, bipolar disorder, post-traumatic stress disorder, attention deficit hyperactivity disorder, and conduct disorder. It has a deep impact on the patient, as well as society. Acts of aggression account for 1.5 million deaths annually worldwide, yet effective treatments for impulsive aggression are very limited. A better understanding of the development of aggressive behavior and the underlying neural circuits will allow for the development of interventions and targeted treatments for excessive aggression found in psychiatric disorders. From recent basic science research, using a novel transgenic mouse model we recently identified a developmental sensitive period for the effect of 5-HT1BR on aggression. Specifically, alterations in 5-HT1BR signaling during the peri-pubertal period lead to increased impulsive aggression in mice throughout life. Now, through epidemiological analysis of longitudinal studies, we will investigate the presence of a similar sensitive period for the development of aggression in humans.