This chapter examines the relationship between impulsive and compulsive disorders as well as select obsessive-compulsive spectrum disorders (OCSDs). OCSD disorders with the strongest association with clinical obesity include binge-eating disorder (BED) and Prader–Willi Syndrome. The chapter reviews the weight gain issues associated with select compulsive, impulsive, and developmental disorders comprising OCSD. Conceptualization of OCSD from a dimensional, rather than categorical perspective, has advanced diagnostic treatment and etiological investigations of many conditions. OCSDs may also share common neurobiological foundations. For example, OCSDs may be characterized on a dimension of serotonin sensitivity and frontal lobe activity, with impulsive disorders characterized by hypofrontality and decreased presynaptic serotonergic levels, and compulsive disorders associated with hyperfrontality and increased serotonergic sensitivity. BED is the only eating disorder associated with obesity. Numerous studies have outlined the occurrence of psychopathology in individuals with BED. obsessive-compulsive disorder is estimated to affect approximately 2.3% of the United States population and its symptomalogy provides the basis for classification of OCSDs.