The MIDJA study is a probability sample of Japanese adults (N = 1,027) aged 30 to 79 from the Tokyo metropolitan area. Survey data were collected on sociodemographic characteristics (age, gender, marital status, educational status), psychosocial characteristics (e.g., independence/interdependence, personality traits, sense of control, goal orientations, social support, family obligation, social responsibility), mental health (depression, anxiety, well-being, life satisfaction), and physical health (chronic conditions, health symptoms, functional limitations, health behaviors). These measures parallel those in a national longitudinal sample of midlife Americans known as MIDUS (ICPSR 4652: MIDUS II and ICPSR 2760: MIDUS I). The central objective is to compare the Japanese sample (MIDJA) with the United States sample (MIDUS) to test the hypothesis that the construct of interdependence predicts well-being and health in Japan, whereas the construct of independence predicts well-being and health in the United States. Cultural influences on age differences in health and well-being are also of interest.