Findings from basic and applied research suggest that treatment with operant extinction may produce adverse side effects; two of these commonly noted are an increase in the frequency of the target response (extinction burst) and an increase in aggression (extinction-induced aggression). Although extinction is often used to treat problem behavior in clinical settings, few applied studies have examined the prevalence of these side effects or their possible attenuation with other operant procedures. An analysis of 41 data sets for individuals who received treatment for self-injurious behavior indicated that extinction bursts or increases in aggression occurred in nearly one half of the cases. The prevalence of bursting and aggression was substantially lower when extinction was implemented as part of a treatment package rather than as the sole intervention.