Attention Deficit and Hyperactivity /Impulsivity Disorder (ADHD) is a highly prevalent neuropsychiatric condition, affecting as many as 1 % of the adult population. The scientific literature suggests that approximately 70 % of patients with ADHD have an additional disorder, making co-morbidity the rule, rather than the exception. Many individuals with ADHD are having more than one co-morbid disorder. The high prevalence of co-morbid psychiatric conditions increases the impairment, and complicates treatment. Furthermore, the societal and medical expenses associated with co-morbid conditions are extensive. The most prevalent co-morbid psychiatric conditions seen in both genders with ADHD are: affective disorders, anxiety disorders, personality disorders and substance use /dependence disorders. It has to be realized that co-morbidity was originally not conceived to signify that a patient had 2, 3, 4 or more psychiatric diagnoses at the same time, but to document the whole symptomatic syndrome in a patient. In this presentation, 100 patients with ADHD in an outpatient facility were consecutively examined with regard to co-morbid conditions. The diagnostic trajectory entailed a semi-structured clinical interview, collateral information, school reports and an extensive neuropsychological battery. Best estimate diagnoses were obtained. Although the results correspond to a large extent with those of similar studies, our sample included a relatively large proportion of patients with co-morbid psychosis. It has been suggested to classify ADHD and psychosis as a separate diagnostic entity. The rationale for this proposal will be discussed.