The literature has stated that all adults with Down syndrome (DS) develop the physiological signs of Alzheimer's disease (AD), but that the behavioural changes may not occur until many years later. While there has been a fair bit of literature on the benefits of leisure in reducing the risk, or delaying the development, of AD in adults without DS, this literature is almost non-existent for the DS population. The purpose of the present study was two-fold. First, this study investigated the differences in cognition, language, and literacy skills, and leisure activity participation in younger and older adults with DS. Second, this study examined leisure activity participation as a predictor of cognitive, language, and literacy abilities. Results showed that older participants (age 46-60) tended to score more poorly on measures of cognition, language, and literacy than younger participants (age 20-45). These age-related differences may, in part, be due to AD. Leisure activity participation was also found to vary with age, such that older adults engaged in fewer physical, cognitive, and social leisure activities and worked more hours than the younger adults. Differences in leisure activity participation may be due to AD or to the participant's place of residence, where participants living in a group home tended to work more and were involved in less leisure than participants living with their parents. Finally, leisure activity participation was not found to predict cognitive, language and literacy scores, with the exception of watching television, which negatively predicted oral expression scores. While true of all adults, adults with DS should be encouraged to dedicate more time to positive leisure activities at all ages, and more specifically to cognitive leisure activities, and dedicate less time to television watching, to help delay the onset of declines associated with AD.