The “secondary gain” concept originated in the psychoanalytic literature, where it was never vigorously examined. The purpose of this review is to determine if there are scientific studies that have explored the validity of this concept.DesignA computer and manual literature review yielded 166 references in which primary, secondary, and tertiary gain were mentioned. Twenty-four (14.5%) of these reports were “secondary gain” studies. Fourteen “reinforcement” studies were also found. These 38 studies were grouped according to topics and reviewed in detail.SettingAny medical treatment setting including pain treatment was utilized in the review procedure, i.e., no exclusion criteria.PatientsAny patient type, including those suffering from chronic pain, were utilized in the review procedure, i.e., no exclusion criteria.ResultsA significant but limited number of studies have investigated the “secondary gain” concept, and the results of some of these studies are in conflict. Results of some studies, however, are remarkably consistent in supporting the importance of “secondary gain” to behavior. Some studies have methodological flaws, usually relating to how the presence of secondary gain was established.ConclusionsOverall the results of the reviewed studies support the potential importance of the “secondary gain” concept to understanding illness behavior and underscore a need for future research in this area.