The purpose of this study was to examine the longitudinal, bidirectional relationship between language skills and behavior problems in a sample of 194 preschool children enrolled in Head Start programs. Children were individually assessed using the "Preschool Language Scale-5," and teachers completed the "Child Behavior Checklist-Teacher Report 1½-5." Cross-lagged path models using a structural equation modeling approach tested the reciprocal associations between language skills and behavior problems over the preschool year. Findings supported a bidirectional relationship between internalizing behavior problems and expressive language skills. However, findings supported a unidirectional association between early receptive language skills and later internalizing behavior problems. Gender moderated the relationship between receptive and expressive language skills and internalizing behavior problems in such a way that the association was only significant for girls. Implications for early intervention and prevention efforts targeting language development and behavior problems were discussed.