RESUMEN
BACKGROUND: Globally, internalizing problems disproportionately affect females in adolescence and adulthood, with limited research at earlier ages due to a focus on disruptive behaviors. Our study addresses this gap by exploring the structure of internalizing problems and gender differences in Brazilian preschoolers. METHODS: We analyzed data from the Child Behavioral Checklist 1.5-5 in the Preschool Mental Health Study, involving 1,292 children aged 4 to 5 in Embu das Artes, São Paulo, Brazil. Confirmatory factor analysis and mean comparisons explored internalizing problems and gender variations. RESULTS: A two-factor model best fit both internalizing and externalizing problems.The hierarchical model with four factors (Emotionally Reactive, Anxiety/Depression, Somatic Complaints, and Withdrawn) best fit internalizing problems, achieving partial invariance between boys and girls. Boys scored higher in Withdrawn Syndrome, while girls scored higher in Somatic Complaints Syndrome. CONCLUSIONS: Preschoolers' internalizing problems warrant attention beyond their link to externalizing problems. While the overall construct is similar in boys and girls, divergent syndrome scores indicate potential distinct risk patterns requiring further exploration.