Developmental trends in type A behavior and somatic risk factors of coronary heart disease were studied in 842 healthy adolescents and young adults. Type A behavior was measured using the AFMS and the somatic risk factors adopted were serum total cholesterol, LDL and HDL cholesterol, systolic blood pressure, diastolic blood pressure, pulse frequency and body mass index. The results showed that cross-sectionally somatic and behavioral risk indicators were independent, but longitudinally an increasing tendency towards type A behavior in boys was related to an increasing level of somatic risk. In boys type A behavior predicted also cross-sectionally a likelihood to be classified into the group where serum cholesterols increased according to age. In girls, no correlation was found.