Background: The positive impact of physical activity on health is widely known. A comparison between activPAL objective measures and International Physical Activity Questionnaire short form (IPAQ-SF) self-reported activity levels was completed with older adults with intellectual disability. Understanding differences between the two methodologies will better support the interpretations of findings and recommendations. Methods: ActivPAL measures including intensity, time and type were considered for 72 participants. Similarly, the IPAQ-determined measures were investigated. Implications of different numbers of activPAL valid days were considered. Comparisons between the activPAL and IPAQ-SF scores were examined using multiple correlation coefficients. Results: Low to moderate agreement was found between the activPAL and IPAQ-SF using Spearman's Rho and Pearson's correlation coefficients. Conclusions: The IPAQ-SF may not be the optimal tool for the accurate determination of activity levels in this population.