Although delusional statements in people with intellectual disabilities and traumatic brain injury can be treated using behavioral interventions, none have demonstrated long-term treatment effects. In the current study, a functional analysis demonstrated that delusional statements were maintained by attention. Differential reinforcement of alternative behavior and extinction of delusional statements resulted in near elimination of delusional statements and an increase in nondelusional statements. Follow-up at 6 months, 1, 2, and 4 years indicated that treatment gains were maintained with continued staff training. (Contains 1 figure.)