Examined were the impact of exercise barriers and carer attitudes regarding exercise outcomes on the exercise participation of adults with Down syndrome (DS). The sample included 44 adults age 30 years and older with DS and mild to moderate intellectual disability and their carers (family members or staff). Measures included personal characteristics of the adults with DS (age, level of adaptive behavior, and health status), carer perceived outcomes of exercise for people with DS, socio-emotional barriers, and access barriers to exercising. A regression analysis was conducted with exercise frequency as the dependent variable and the above measures as the independent variables. The significant determinants of exercise participation were carers' perceived outcomes of exercise for persons with DS and access barriers. When carers perceived greater benefits of exercise and when there were fewer access barriers, the adults with DS were likely to exercise more frequently. Persons with DS were more likely to report access barriers than were informants. The results reinforce the need to improve access to exercise facilities and equipment and to increase carers' awareness of the importance of exercise for adults with DS.