Objective: Personality characteristics are found to be related with substance use initiation, substance abuse, substance dependence and substance use continuance. The aim of this study is to investigate the personality characteristics of adolescents with alcohol/substance use disorder (ASUD). Methods: Sixty-nine adolescents with ASUD, aged between 16 and 18 were compared with 69 adolescents with similar sociodemographic properties and without ASUD. Minnesota Multiphasic Personality Inventory (MMPI) was used to assess personality traits. Results: Adolescents with SUD had higher scores for psychopathology (F), hypochondriasis, hysteria, depression, psychopathic deviation, paranoia, psychasthenia, schizophrenia, and hypomania scales and lower score for defensiveness (K) scale when compared with the control group. Discussion: Adolescents with ASUD have insufficient defense mechanisms and negative personality characteristics. Personality characteristics of these adolescents should be considered in the treatment and follow up periods.