The validity of selecting treatment contingencies on the basis of the results obtained through functional analysis is well documented. However, a number of second-generation questions have emerged: For example, what are the parameters required to achieve desired treatment outcomes? More specifically, what is the degree of treatment integrity needed for the successful reduction of problem behavior? This study had two purposes: to describe the relationship between treatment integrity levels and treatment effectiveness and to highlight the importance of reporting the treatment integrity in outcome-based research. The results indicate that a high level of treatment integrity is required for treatment success. Furthermore, the authors found that very low levels of integrity may be required for behavioral reduction procedures (i.e., extinction) if high levels of reinforcement are provided. (Contains 5 figures.)