Noncontingent reinforcement (NCR) is a commonly used treatment for severe problem behavior displayed by individuals with intellectual and developmental disabilities. The current study sought to extend the literature by reporting outcomes achieved with 27 consecutive applications of NCR as the primary treatment for severe problem behavior. All applications of NCR were included regardless of treatment outcome to minimize selection bias favoring successful cases. Participants ranged in age from 5 to 33 years. We analyzed the results across behavioral function and with regard to the use of functional versus alternative reinforcers. NCR effectively treated problem behavior maintained by social reinforcement in 14 of 15 applications, using either the functional reinforcer or alternative reinforcers. When we implemented NCR to treat problem behavior maintained by automatic reinforcement, we often had to add other treatment components to produce clinically significant effects (five of nine applications). Results provide information on the effectiveness and limitations of NCR as treatment for severe problem behavior.