A defining feature of autism spectrum disorders is atypical behaviors, e.g., stereotypy, noncompliance, rituals, and aggression. Deaf and hard of hearing individuals with autism present a greater challenge because of additional issues related to their hearing status. One conceptualization of problem behavior is that it serves a communication function, i.e., the person has learned that certain misbehaviors may be reinforced in some way. The present article describes "functional behavior assessment," a group of state-of-the-art methodologies that allow a caregiver to determine the cause of the behavior, so that treatment--based on that cause--will be more effective. Different methods of functional assessment are described, along with a step-by-step implementation sequence. The results of a functional assessment should lead to more effective programming, resulting in quicker elimination of the behavioral concerns, and allow the person to gain access to greater independence and more reinforcement.