When evaluating the effectiveness of sex offender treatment, several issues must be considered, as well as the strengths and weaknesses to all of the various methods. Opinions differ in terms of the extent of methodological flaws that should be permitted. It is generally agreed by both optimists and skeptics, that good treatment evaluation designs are those that include a treated and a comparison group equated in terms of risk. The effectiveness of sex offender treatment has been studied and reviewed extensively over the years. However, criticisms exist of all the various methodologies used to date in studies of treatment effectiveness looking strictly at recidivism outcome. Some have suggested additional ways the effectiveness of treatment could be established, by examining not only ultimate outcomes of interest but proximate outcomes, and examining within treatment change providing a more complete picture of effectiveness. The aim of this paper is to discuss various methods of examining treatment effectiveness. It describes a number of research methods used to examine the overall effectiveness of sex offender treatment, such as random assignment, risk band analysis, matched control groups, and change within treatment. Tables, references