Although high anxiety is common in people with intellectual disabilities (ID) and the anxiolytic effects of exercise have been systematically recognised in clinical and non-clinical populations, research is scant concerning the role played by exercise on anxiety in people with ID. The purpose of this study was to investigate the effects of a 12-week exercise programme on anxiety states in a group of adults with ID. Twenty-seven individuals with mild to moderate ID were randomly assigned to an exercise group or a control group. The Zung Self-Rating Anxiety Scale adapted for individuals with ID and the State-Trait Anxiety Inventory form Y were used to assess trait and state anxiety. In comparison with the control group, the anxiety scores of people in the exercise group decreased significantly over time.