We assessed conjoint trajectories of cognitive decline and social relations over 7 years on a representative sample of community-dwelling elderly persons. We analyzed data using repeated measurement models. Social integration, family ties, and engagement with family were associated with cognitive function at advanced ages, controlling for education and introducing depressive symptoms, functional limitations, and chronic conditions as intervening variables. Association of social integration, through participation in community activities, with change in cognitive decline was more significant at advanced ages. Having friends was significantly associated with change in cognitive function in women only. Our findings have important implications for clinical medicine and public health because associations of social relations with cognitive function suggests that they may help to maintain cognitive function in old age.