55 suicidal adolescent inpatients were compared with 87 adolescent inpatients with no history of suicide ideation or attempts & 81 nonpatients. Defense mechanisms were assessed using the Ego Defense Scale, the Child Suicide Potential Scale & a self-report questionnaire. Overuse of displacement was connected with increased risk for suicidal & aggressive behaviours while sublimation was a probable protective factor. It is suggested that several immature ego defenses possibly amplify aggression.