Some boys experienced the preschool program and some did not, and this allowed the authors to test whether the program had any effects on risk for early adolescent delinquency given their perinatal histories. The research hypothesized that perinatal complications would place boys at significantly greater risk for antisocial behavior during adolescence, and that participation in a preventive preschool program might circumvent this risk. The preventive preschool program was offered to low-income children with the aim of promoting academic success. Independent of maternal sociodemographic characteristics, boys with a history of perinatal complications showed no greater risk of delinquency during early adolescence than their peers without a history of perinatal complications. Surprisingly, the preschool program had a beneficial effect on boys with no history of serious perinatal complications, and such boys were less at risk for delinquency. In the presence of a serious medical condition after birth, benefits of the preschool program decreased significantly to the point that it placed boys at risk. 60 references, 4 tables, and 1 figure