Background: It has been reported in the literature that people with an intellectual disability (ID) are less physically active, live more sedentary lives, have lower fitness levels and are more likely to be overweight or obese than the general population. Nine thousand people with ID are participating in Special Olympics Ireland (SOI). To date, no evidence exists on the impact of SOI participation on physical activity (PA) and physical fitness levels of adults with ID’s in Ireland. Methods: Adults with ID (16-64 years) were recruited from 4 ID services and SOI clubs throughout Ireland (n=146, male 85, female 61). Both SOI participants and non SOI participants were invited to participate. Physical measures included waist circumference, height, weight, blood pressure, heart rate and the Six Minute Walking Test. Self-report questionnaires were administered to study participants to gather data on PA levels. To get an objective measure of PA, participants were asked to wear an Actigraph (GT3X) accelerometer for seven consecutive days. Results: Self-report data suggests SOI participants accumulated significantly more mean minutes moderate to vigorous physical activity (MVPA) daily than non-SOI participants (p = .002). SOI participants also recorded more minutes of accelerometer measured MVPA on average daily than non-SOI participants, however differences were not statistically significant. Significantly greater distances were walked in the Six Minute Walk test by SOI participants compared to non-SOI participants (p = .000), and those in SOI had a significantly more positive health profile score than those not in SOI (p = .013). Conclusion: Participants in SOI accumulated significantly more minutes of MVPA per day, had higher fitness levels, and more positive health profile scores than non-SOI participants. SOI has the potential to make a positive difference to people’s physical health and subsequently their overall health and wellbeing.