This article addresses the following questions: (1) How to distinguish dissociative identity disorder (DID) from a variety of other mental disorders, including schizo- phrenia and other psychotic disorders, bipolar disorder, anxiety disorders and personality disorders?, and (2) How to distinguish DID from malingering and from factitious disorder? Systematic assessment of five dissociative symptom areas with the SCID-D (Steinberg 1993) facilitates the assessment of the presence and type of dissociative disorder. Based on research, the characteristic cluster of dissociative symptoms and associated features of DID is described, as well as the differentiation from other mental disorders. The issues of under- and overdiagnosis are addressed. It is concluded the DID can be well distinguished from resembling and factitious disorders, provided that the dissociative symptoms are systematically assessed.