Sexuality research focuses almost exclusively on individuals rather than couples, though ongoing relationships are very important for most people and cultures. The present study was the first to examine sexual and relationship parameters of middle-aged and older couples in committed relationships of 1-51 years duration. Survey research was conducted in Brazil, Germany, Japan, Spain, and the U.S. targeting 200 men aged 40-70 and their female partners in each country, with 1,009 couples in the final sample. Key demographic, health, physical intimacy, sexual behavior, sexual function, and sexual history variables were used to model relationship happiness and sexual satisfaction. The median ages were 55 for men and 52 for women; median relationship duration was 25 years. Relationship satisfaction in men depended on health, physical intimacy, and sexual functioning, while in women only sexual functioning predicted relationship satisfaction. Models predicting sexual satisfaction included significant physical intimacy and sexual functioning for both genders and, for men, more frequent recent sexual activity and fewer lifetime partners. Longer relationship duration predicted greater relationship happiness and sexual satisfaction for men. However, women in relationships of 20 to 40 years were significantly less likely than men to report relationship happiness. Compared to men, women showed lower sexual satisfaction early in the relationship and greater sexual satisfaction later. Within the long-term committed relationship context, there were significant gender differences in correlates of sexual and relationship satisfaction, with sexual functioning a common predictor of both types of satisfaction and physical intimacy a more consistent and salient predictor for men.