Instruments that are used for diagnosing of, or screening for, autism spectrum disorder (ASD) may not be applicable to people with sensory disabilities in addition to intellectual disabilities. First, because they do not account for equifinality, the possibility that different conditions may lead to the same outcome. Second, because they do not have appropriate norms for this target population. The current study reviewed 20 instruments commonly used in the assessment of screening for and diagnosing ASD. Reviewed were: purpose, number of items, psychometric properties (norms, reliability, and validity), test availability, and item applicability for people with sensory and intellectual disabilities. Most instruments did not have norms for the target population and all instruments consisted of a quarter or more of invalid items. When using current instruments, caution is required in interpreting test results. For proper assessment of ASD in people with sensory and intellectual disabilities, more instruments are needed that are adapted to the sensory and intellectual disabilities of this population.