The influence of self-reported and informant-reported activity levels on Crystallized Intelligence, Fluid Intelligence, Memory and the Mini-Mental State Examination was investigated in a sample of 858 community-dwelling elderly subjects. Both self-reported and informant-reported activity levels explained variance beyond that accounted for by sex, sensory functioning, activities of daily living, medical conditions, current health problems and education. Age accounted for additional variance once activity and the other contextual variables were entered. Interaction effects indicated that inactivity was associated with poorer performance on fluid intelligence in older rather than younger elderly subjects and that inactivity was predictive of poor crystallized intelligence at younger ages. Higher informant-rated activity levels moderated the effects of education, so that higher activity offset effects associated with low education on memory tasks. The mount of variance explained by activity levels was modest.