Previous studies of sexual behavior in middle and late life suggest a decline in sexual activity during the last half of adulthood. Longitudinal data on the sexual activity of 278 married men and women, initially aged 46 to 71 years, were collected. These data suggest that levels of sexual activity remain more stable over time than previously suggested. It is crucial to distinguish between aggregate trends and intraindividual change. Although stable levels of sexual activity are typical, aggregate statistics can blur distinct patterns of change exhibited by individuals. Special attention is paid to the relative influences of age, cohort, and gender on sexual activity during middle and late life.