Background: Leisure activity has been linked to optimal ageing outcomes, yet little is known about the type and level of leisure activity adults with Down syndrome currently engage in, and the factors that promote and hinder their leisure activities. Materials and Methods: A daily diary was utilized to provide an in-depth description of the average daily leisure activity of 44 adults with Down syndrome (aged 25-56 years) across a typical 7-day period. Factors related to participation, including initiators, social partners, settings and barriers, were examined. Results: Findings indicated that the majority of adults with Down syndrome did not meet established physical leisure activity intensity recommendations (i.e., 150 min/week moderately active activity) and did not exceed levels of passive leisure (e.g., watching television) found in the general population (i.e., 2-3 hr/day). Adults with Down syndrome self-initiated and self-engaged in the majority of their leisure activity. Family members and paid staff allocated resources towards initiating and engaging as social partners in social and physical leisure, respectively. Conclusions: Interventions and support services should partner with family members and paid staff to foster participation in adaptive leisure activity, perhaps through the establishment of leisure activity as part of daily routines.