Coital frequency is studied among couples as a function of marital or cohabiting status, relationship duration, number of children, religious affiliation, income, education, fertility intentions, age, race, self-assessed health, time spent in work, and perceived relationship quality. Data are from the 1987–88 National Survey of Families and Households. Predictors of coital frequency that were stable across several analyses were male's and female's ages, the duration of the relationship, and the male partner's self-assessed health. When the discrepancy in partners' reports was adjusted, cohabitation status, number of children, future fertility intentions, religious affiliation, and relationship quality as assessed by the female partner were significant. The results suggest a substantial idiosyncratic component to the determination of coital frequency in relationships.