Objective: To examine sex differences in the rate andsymptoms ofposttraumatic stress disorder (PTSD), trauma exposure, and onset patterns in youth with conduct disorder (CD).Method: Youth admitted to a clinicalfacility for severe behaviour problems completed the Diagnostic Interview for Children and Adolescents -Revised (DICA-R) . Studies demonstrate elevated rates of PTSD in delinquent adolescents and young adults, presumably because exposure to trauma potentiates both delinquent behaviour and PTSD. For example, in a study of incarcerated male juvenile offenders, Steiner and others found that over one-half of the participants fulfilled partial (20%) or full (32%) criteria for PTSD (1). They noted that these rates far exceeded those found in a nonclinical adolescent comparison group. Male juvenile offenders most frequently reported traumatic events involving interfamilial violence (for example, abuse, murder, or serious injury) and exposure to community violence (gang-related activities). In a subsequent study, Cauffman and others found that approximately two-thirds of the incarcerated female juvenile offenders they studied met partial (12%) or full (49%) criteria for PTSD (2). These rates were significantly higher than those noted for comparable male juvenile offenders. Further, compared with male offenders, female offenders more frequently reported being victims ofviolent acts (51%; 15% for males) rather than witnesses to such acts (17%; 48% for males).Although delinquency and conduct disorder (CD) are not interchangeable terms, it is generally agreed that there is substantial overlap. Both CD and PTSD show strong associations with other psychiatric conditions. Although research shows that CD can occur in isolation, it occurs most frequently in conjunction with Axis I disorders, including attention-deficit hyperactivity disorder, depression, anxiety disorders, and substance use disorders (3-8), and Axis II personality disorders (9). Researchers have also consistently reported that PTSD is associated with various psychiatric conditions (10). Axis I disorders that are frequently comorbid with PTSD include depression (11,12), anxiety disorders (13,14), substance use disorders (15), and eating and somatization disorders (16). Comorbid Axis II disorders, including borderline personality disorder, have also been noted (17). Since CD and PTSD each carry a high level ofcomorbidity on both Axis I and Axis II, the association between them poses a challenge for researchers and clinicians.Sex differences in the clinical presentation of PTSD and CD further complicate efforts to understand comorbidity between these disorders. Well-established is the sex difference in the prevalence of CD-while it is predominantly a male disorder (4,18), it is the second most prevalent psychiatric