To evaluate the relationship between plasma serotonin (p5-HT) levels and psychometric measures in suicidal adolescents vs. controls, 211 adolescents from three sites in Israel were divided into four groups: suicidal psychiatric inpatients (n=35); non-suicidal psychiatric inpatients (n=30); adolescents referred to the emergency room (ER) due to a suicide attempt (n=51); and a community-based control group from 4 high schools in the same catchment areas (n=95). All were interviewed and assessed for violence, aggression, depression, impulsivity, anger, anxiety, and p5-HT. p5-HT levels were significantly lower in the control group compared to all other groups. A significant negative correlation was found between p5-HT level and suicidal behavior severity among the suicidal inpatients. p5-HT did not discriminate between the psychiatric diagnostic categories and was significantly lower in ER violent compared to non-violent subjects. Gender, depression, and anger were associated with suicidal behavior in all four groups. Beck Depression Inventory (BDI) scores together with p5-HT levels discriminated between healthy controls and other groups. p5-HT level in combination with some of the psychometric scales may serve as a safe and inexpensive peripheral marker of psychopathology, and may help to differentiate between sub-populations of suicidal adolescents. The biological mechanism behind the serotonin dysregulation in suicidal adolescents requires further investigation.