This study investigated age differences in multiple aspects of psychological well-being among midlife and older adults in Japan (N = 482) and the United States (N = 3,032) to test the hypothesis that older Japanese adults would rate aspects of their well-being (personal growth, purpose in life, positive relations with others) more highly that older U.S. adults. Partial support was found: older adults in Japan showed higher scores on personal growth compared to midlife adults, whereas the opposite age pattern was found in the United States. However, purpose in life showed lower scores for older adults in both cultural contexts. Interpersonal well-being, as hypothesized, was rated significantly higher, relative to the overall well-being, among Japanese compared to U.S. respondents, but only among younger adults. Women in both cultures showed higher interpersonal well-being, but also greater negative affect compared with men. Suggestions for future inquiries to advance understanding of aging and well-being in distinct cultural contexts are detailed. (Contains 2 tables and 3 figures.)