This paper applies a developmental structuralist approach to the classification of adaptive and pathologic personality organizations and behavior in infancy and early childhood, and it discusses implications of this approach for preventive intervention. In general, as development proceeds, the structural capacity of the developing infant and child enlarges, and higher level integrating and synthesizing capacities emerge. The major assumption of a developmental structuralist approach is that the infant is capable of organizing experience at birth and that as development proceeds this capacity becomes more adaptive in regard to organizing phase-appropriate experience of a progressively greater range, stability, resilience, and uniqueness. A detailed developmental structuralist classification scheme for infancy and early childhood may be described according to stage-specific tasks. Achieving homeostasis, forming a human attachment, somato-psychological differentiation, behavioral organization, initiative, and internalization, and forming mental representations are the stages and capacities or tasks in the developmental structural model proposed. Illustrating the usefulness of this approach for understanding psychopathology and adaptation in infancy and early childhood, the stages of (1) somato-psychological differentiation and (2) behavioral organization, initiative and internalization are discussed in terms of adaptive patterns, defects or disorders, adaptive and disordered environments and prevention and treatment. (Author/RH)