The diagnostic framework presented in this manual seeks to address the need for a systematic, multi-disciplinary, developmentally based approach to the classification of mental health and developmental difficulties in the first 4 years of life. An introduction discusses clinical approaches to assessment and diagnosis, gives an overview of the classification system, and offers guidelines for diagnosis. In the classification, the focus is on developmental issues with dynamic processes, such as relationships and developmentally based conceptualizations of adaptive patterns of central importance. The diagnostic framework consists of five axes: Axis 1--primary classification (e.g., disorders of affect, anxiety disorders, mood disorders, sleeping and eating behavior disorders); Axis 2--relationship disorder classification (e.g., overinvolvement, underinvolvement, anger/hostility, abuse, sexual abuse); Axis 3--medical and developmental disorders and conditions; Axis 4--psychosocial stressors; and Axis 5--functional emotional developmental level. Appendices include the Parent-Infant Relationship Global Assessment Scale, descriptive criteria for patterns of multi-system developmental disorder, and an outline of the classification system. Seventeen case vignettes are provided, as is an index to primary diagnoses of cases. (CR)