Our aim was to identify risk factors for falling and establish a method to assess risk for falls in adults with intellectual disabilities. In a cross-sectional survey of 144 Japanese adults, we found that age, presence of epilepsy, and presence of paretic conditions were independent risk factors. The Tinetti balance and gait instrument was successfully administered to this population and resulted in high diagnostic accuracy (sensitivity 88.9%, specificity 91.9%) for identifying individuals at risk when the cutoff score was set at 25. Participants whose balance and gait deteriorated showed a decrease in the Tinetti score of at least 2 points per year. Thus, the Tinetti instrument may be an effective tool to detect an increased risk of fall in this population.