People with intellectual disability (ID) are reported as a sedentary population with increased risks of poor health due to an inactive and sedentary lifestyle. As the benefits of physical activity are acknowledged, measuring physical activity accurately is important to help identify reasons for low and high physical activity in order to assist and maintain recommended levels for optimal health. This article reports a pilot study undertaken to validate the use of a physical activity monitor (Sensewear Armband) and the International Physical Activity Questionnaire (IPAQ) as instruments for measuring and exploring physical activity of men with ID. The design was a one-group descriptive study and the data were collected over a 7-day period from 17 men. The Sensewear Armband enabled continuous and long-term measurement of 14 objective physical activity metrics. The IPAQ examined details of physical activity reported over 7 days. Equivalent results were obtained from both the instruments, indicating a positive correlation between the Sensewear Armband and the IPAQ. The results show 50% have low activity levels, and the national recommended physical activity levels have been achieved at a very low active intensity. No sustainable high physical activity intensity levels were recorded. The results confirmed the Sensewear Armband and the IPAQ as a practical means of measuring and understanding physical activity levels in men with ID.