The association of apolipoprotein E (apoE) polymorphism with temperament and Type A behavior was studied in 1577 randomly selected healthy children, adolescents, and young adults during a follow-up period of 9 years. Temperament was correlated with apoE phenotypes. Motor activity, even hyperactivity, in childhood and mental vitality in adolescence and young adulthood increased significantly with the apoE phenotypes in the order of E2/2, E3/2, E4/2, E3/3, E4/3, and E4/4. However, global Type A behavior was not associated with the order of apoE phenotypes. The findings suggest the importance of additional studies on genetic factor and temperament.