This study examined the prediction of different forms of adult aggression in 2 countries from child and adolescent aggression. It was based on 2 longitudinal projects: the Jyväskylä Longitudinal Study of Personality and Social Development (JYLS; N=196 boys and 173 girls) conducted in Finland and the Columbia County Longitudinal Study (CCLS; N=436 boys and 420 girls) conducted in the United States. The same peer‐nominated items for aggression were used in both studies at age 8; comparable measures of aggression were also available in adolescence (age 14 in the JYLS/19 in the CCLS) and adulthood (ages 36/30 and 42/48). Results showed that in both countries and in both genders, aggression in school age was linked significantly to physical aggression and lack of self‐control of anger in adulthood but not to verbal aggression. This differential predictability of aggression over 40 years suggests that individual differences in physical aggression are more determined by lasting individual differences (including emotional reactivity) than are individual differences in verbal aggression.