Objective: The aims of this paper are as follows: to present past-year prevalence data for DSM-IV disorders in the early elementary school years; to examine the impact of impairment criteria on prevalence estimates; to examine the relation of sociodemographic and psychosocial risk factors to disorders; and to explore associations between "internalizing" and "externalizing" disorders and social competence and family burden as further validation of the impairing nature of these disorders. Method: As part of a longitudinal representative population study of children born healthy between July 1995 and September 1997 in the New Haven-Meriden Standard Metropolitan Statistical Area of the 1990 Census (n = 1,329), parents of a subsample enriched for child psychopathology (n = 442; 77.6% response rate, 69.5% of eligible sample) were interviewed in the child's kindergarten or first-grade year with the Diagnostic Interview Schedule for Children, Version IV (DISC-IV). Parents were surveyed about sociodemographic and psychosocial characteristics, and both parents and teachers were surveyed about social competence. Results: Approximately one in five (21.6 %) children met criteria for psychiatric disorder(s) with impairment. Sociodemographic and psychosocial correlates included persistent poverty beginning in early childhood, limited parental education, low family expressiveness, stressful life events, and violence exposure. Finally, diagnostic status was significantly associated with poorer social competence and family burden. Conclusions: That approximately one in five children evidenced a psychiatric disorder with impairment during the transition to formal schooling highlights the importance of integrating psychiatric epidemiological and developmental approaches to inform conversations about school readiness and intervention planning. (Contains 1 figure and 5 tables.)