[Delusional misidentification syndromes].

According to ICD-10 and DSM-IV classifications, delusional misidentification syndromes are a specific subgroup of unspecified persistent delusional disorders. They are characterized by systematic incorrect identification and the basic delusional idea--the concept of a double, illusion of a double. The authors present the most frequent delusional misidentification syndromes, and the most frequent elements of the clinical picture and etiological hypotheses. Because of their small frequency and the basic characteristics of these syndromes to appear mostly as a part of some other disturbance, the authors emphasize the importance of a careful differential diagnostic procedure, which has therapeutic implications.