The distinction between normality and psychopathology has long been subject to debate. DSM-III and DSM-IV provided a definition of mental disorder to help clinicians address this distinction. As part of the process of developing DSM-V, researchers have reviewed the concept of mental disorder and emphasized the need for additional work in this area. Here we review the DSM-IV definition of mental disorder and propose some changes. The approach taken here arguably takes a middle course through some of the relevant conceptual debates. We agree with the view that no definition perfectly specifies precise boundaries for the concept of mental/psychiatric disorder, but in line with a view that the nomenclature can improve over time, we aim here for a more scientifically valid and more clinically useful definition.