We compared the effectiveness of two extinction interventions, extinction by omission and noncontingent delivery of reinforcement, to treat aggressive behavior with a 10-year-old boy. Before the intervention, a functional analysis revealed that aggression was maintained by positive reinforcement in the form of attention. The extinction by omission intervention consisted of ignoring aggressive behavior. Noncontingent reinforcement involved delivering attention to the boy on a fixed-time schedule. Both treatments were compared using a multielement research design. Noncontingent reinforcement produced a more rapid elimination of aggression. Additionally, the schedule of noncontingent reinforcement was gradually thinned during the intervention. Finally, both parents successfully implemented the noncontingent schedule of reinforcement independently for up to 5 weeks after treatment.