Gender differences observed in interpersonal and self-critical vulnerabilities, reactivity to stressful life events, quality of relationships, and self-concepts inform a multivariate theoretical model of the moderating effects of gender on internalizing and externalizing problems in adolescence. To test this model, data were collected in a 1-year prospective study from an ethnically diverse sample of 460 middle school students. Increases in girls' internalizing symptoms, compared with boys', were partly explained by greater stability in girls' interpersonal vulnerabilities and greater magnitude in coefficients linking girls' relationships with parents and peers and internalizing problems. Boys' risks for externalizing problems, compared with girls', were partly explained by the greater stability in boys' vulnerability to self-criticism. Coefficients for most pathways in the model are similar for boys and girls.