Sexual health research tends to focus on problematic aspects of sexuality. This also applies to research on sexuality in older men and women, where attention has been primarily on the negative impact of aging. To contribute to the emerging interest in positive (successful) sexual aging, we aimed to: (1) further validate a recently developed 5-dimensional measure of sexual well-being (Štulhofer et al. in J Happiness Stud, 2018. https://doi.org/10.1007/s10902-018-0049-1) and (2) explore the structure of associations among emotional intimacy, frequency of sexual intercourse, and sexual well-being in older European couples. Using data from a 2016 community-based survey of 218 Norwegian, 207 Danish, 135 Belgian, and 117 Portuguese couples aged 60–75 years, we applied actor–partner interdependence structural modeling approach to confirm the validity of the sexual well-being measure in couples and explore a path analytic model in which the frequency of sexual intercourse was hypothesized to mediate the association between emotional intimacy and sexual well-being. Although we observed consistent and significant actor effects, with emotional intimacy and frequency of sexual intercourse predicting both male and female partners’ sexual well-being across countries, the proposed mediation was observed only in Norwegian and Portuguese men and Norwegian and Belgian women. Partner effects were gender-specific; male partner’s emotional intimacy was related to his female partner’s reported frequency of sex and sexual well-being but not the other way around. Apart from being one of the few cross-cultural assessments of successful sexual aging, this study’s findings support the use of a new sexual well-being measure in research on older adults’ sexuality.