The latest studies on psychopathology and biology of attacks and other findings related to sleep in panic disorder are reviewed. While some of the newer articles doubt that nocturnal panics present a more severe variation of panic disorder, older studies and some newer articles support this notion. Some studies suggest that nocturnal panic maybe also be associated with other, more severe pathology. This interesting syndrome, or variant of disorder, may have its own etiology, psychopathology, and underlying biology. (C) 2003 Wiley-Liss, Inc.