In this chapter, we compare the sexes on disorders and psychiatric conditions that co-occur with antisocial disorders during the developmental period from ages 11 to 21. We examine mental retardation, reading retardation, attention deficit-hyperactivity disorder (ADHD), anxiety disorders, depression and dysthymia, mania, eating disorders, alcohol and marijuana dependence, and schizophreniform symptoms. The chapter addresses three issues. How common is comorbidity among young people who have conduct disorder? What is the pattern of cumulative co-occurrence of conduct disorder with other disorders across the period of the life span we study, and does this pattern differ for males and females? Are there changing patterns of comorbidity with conduct problems across the repeated assessments of the study, and do those patterns differ for males and females?

In recent years awareness has increased about the phenomenon of comorbidity, the concurrent diagnosis of two or more mental disorders within the same individual. Epidemiological studies show that approximately half of all persons with a mental disorder have more than one diagnosable disorder (Clark, Watson, and Reynolds, 1995). The ubiquity of comorbidity has implications for research methodology, clinical practice, and diagnostic nosologies (Caron and Rutter, 1991; Angold, Costello and Erkanli, 1999). With respect to research methodology, it has been shown that comorbidity can confound developmental studies of the onset and course of a disorder (Sher and Trull, 1996).