['Anxiety disorders such as posttraumatic stress disorder (PTSD) and substance use disorders (SUD) are increasingly recognized as comorbid disorders in children with bipolar disorder (BPD). This study explores the relationship between BPD, PTSD, and SUD in a cohort of BPD and non-BPD adolescents.', 'We studied 105 adolescents with BPD and 98 non-mood-disordered adolescent controls. Psychiatric assessments were made using the Kiddie Schedule for Affective Disorders and Schizophrenia-Epidemiologic Version (KSADS-E), or Structured Clinical Interview for DSM-IV (SCID) if 18 years or older. SUD was assessed by KSADS Substance Use module for subjects under 18 years, or SCID module for SUD if age 18 or older.', 'Nine (8%) BPD subjects endorsed PTSD and nine (8%) BPD subjects endorsed subthreshold PTSD compared to one (1%) control subject endorsing full PTSD and two (2%) controls endorsing subthreshold PTSD. Within BPD subjects endorsing PTSD, seven (39%) met criteria for SUD. Significantly more SUD was reported with full PTSD than with subthreshold PTSD (chi(2) = 5.58, p = 0.02) or no PTSD (chi(2) = 6.45, p = 0.01). Within SUD, the order of onset was BPD, PTSD, and SUD in three cases, while in two cases the order was PTSD, BPD, SUD. The remaining two cases experienced coincident onset of BPD and SUD, which then led to trauma, after which they developed PTSD and worsening SUD.'] Do posttraumatic stress disorder and substance use disorder in adolescent bipolar disorder?