Many preschool-age children meet criteria for psychiatric disorders, and rates approach those observed in later childhood and adolescence. However, there is a paucity of longitudinal research examining the outcomes of preschool diagnoses.

Families with a 3-year-old child (N = 559) were recruited from the community. Primary caregivers were interviewed using the Preschool Age Psychiatric Assessment when children were 3 years old (n = 541), and, along with children, using the Schedule for Affective Disorders and Schizophrenia for School-Age Children Present and Lifetime Version when children were 9 and 12 years old.

Rates of disruptive behavior disorders (DBD) decreased from preschool to middle childhood and early adolescence, whereas rates of attention-deficit/hyperactivity disorder (ADHD) increased. Rates of any psychiatric disorder and depression increased from preschool to early adolescence only. Preschoolers with a diagnosis were over twice as likely to have a diagnosis during later periods. Homotypic continuity was present for anxiety disorders from preschool to middle childhood, for ADHD from preschool to early adolescence, and for DBD through both later time points. There was heterotypic continuity between preschool anxiety and early adolescent depression, and between preschool ADHD and early adolescent DBD. Dimensional symptom scores showed homotypic continuity for all diagnostic categories and showed a number of heterotypic associations as well.

Results provide moderate support for the predictive validity of psychiatric disorders in preschoolers. Psychopathology in preschool is a significant risk factor for future psychiatric disorders during middle childhood and early adolescence.

The clinical and etiologic implications of comorbid psychiatric and substance-use disorders are relevant across countries and cultures. The DSM-IV now places greater emphasis on the clinical and research utility of the substance-induced disorders classification, and clarifies several important diagnostic issues specific to primary and substance-induced disorders. However, no research consensus exists over the core problem of identifying and differentiating the drug and alcohol intoxication and withdrawal symptoms that can mimic psychiatric symptoms in heavy drinkers and drug users.

To investigate how various diagnostic instruments have measured comorbid psychiatric and substance-use disorders and how each instrument operationalizes the DSM-IV classification.

We review the evolution of the concept of comorbidity beginning with its formalization as the ‘primary–secondary’ distinction in the Feighner Criteria. We address the ‘organic–non-organic’ distinction found in the RDC, DSM-III, and DSM-III-R; and finally, review the ‘primary’ and ‘substance-induced’ categories of DSM-IV, DSM-IV-TR and ICD-10. We describe how these distinctions have been operationalized in widely used diagnostic instruments.

Further understanding of these classifications and the relationship of co-occurring psychiatric and substance disorders can be accomplished with the range of available measures, particularly the Psychiatric Research Interview for Substance and Mental Disorders (PRISM), which reliably utilizes and refines DSM-IV classification distinctions.