Associations among internalizing, externalizing, and social competence were examined in a longitudinal cohort (N = 205) of 8- to 12-year-old children reassessed after 7, 10, and 20 years. Theoretically informed nested structural equation models tested interconnections among broad multi-informant constructs across four developmental periods. Follow-up analyses examined gender invariance, measurement and age effects, and putative common causes. Key model comparisons indicated robust negative paths from social competence to internalizing problems from childhood to adolescence and from emerging adulthood to young adulthood. Social competence and externalizing problems showed strong initial associations in childhood but no longitudinal cross-domain paths. Using a developmental psychopathology framework, results are discussed in relation to cascade and transactional effects and the interplay between competence and symptoms over time.