We examined the prevalence and course of psychiatric and substance dependence (SD) disorders in subjects with SD and attention deficit hyperactivity disorder (ADHD).Method-We interviewed 1,761 adults with a lifetime diagnosis of cocaine and/or opioid dependence using the Semi-Structured Assessment for Drug Dependence and Alcoholism. Generalized linear regression with generalized estimating equation analysis was used to examine the associations between a lifetime diagnosis of ADHD and indicators of clinical course, and to identify unique correlates of ADHD.Results-Lifetime ADHD prevalence in the SD sample was 5.22% (vs. 0.85% in a group of individuals without SD). ADHD was associated with an earlier age of first substance use, more SD and psychiatric diagnoses, a greater likelihood of attempted suicide, and more hospitalizations. After controlling for conduct disorder and bipolar type I disorder, there were unique effects of ADHD on age of first substance use and number of SD diagnoses.Conclusion-In subjects with cocaine or opioid dependence, ADHD is associated with greater SD and psychiatric comorbidity and a more severe course of illness.