It has been found that a significant improvement in personality disturbances of paranoid personality, borderline personality and avoidant personality types, as a response to Serotonin Reuptake Inhibitors (SSRI) specially Sertraline. The serotoninergic disturbed functions with the central nervous system could be the basis of impulsive aggression and self destructive behaviour expressed by patients with personality disorders. The article discusses the case of a 37-year old male patient. At age 23,he was involved in a car accident and sustained a serious head injury which he never received any psychiatric treatment. The psychiatric evaluation of the patient revealed personality disorder of posttraumatic type. No family history of psychiatric disorder could be detected. The patient was treated with individual psychotherapy and Sertraline with satisfactory remission of the symptoms. SSRIs have been used in the treatment of patients who developed irritability and aggression following closed head traumSertraline has been shown to be effective in the treatment of impulsive aggression in patients with personality disturbances. It has been claimed that the effectiveness of Sertraline can be explained by the sedative effect of the drug