The tripartite model of anxiety and depression has been studied with adults; however, support is still emerging with children concerning measurement and relations between positive (PA) and negative (NA) affect and psychopathology. In this longitudinal study of 270 4th- to 11th-grade children (mean age = 12.9 years, SD = 2.23). confirmatory factor analysis supported a 2-factor orthogonal model of children's self-reported affect and revealed that the concurrent relations of NA and PA to anxiety and depression symptoms were consistent with the tripartite model. Structural equation modeling demonstrated moderate cross-time stability of trait PA and NA, consistent with a temperament view of these factors, as well as partial support for the role of NA and PA in the development of anxiety and depression symptoms in children.