Lycanthropy is an unusual belief or delusion that one has been transformed into an animal, or behaviors or feelings suggestive of such a belief. We report a case of lycanthropic delusions of becoming a snake in a 47-year-old woman who suffered from a major depressive disorder with psychotic features. We also present a literature review of articles published on the subject in English or French since 1975 identified via a MedLine search using the terms "lycanthropy" or "werewolf." Many case reports have described lycanthropy as a delusional disorder occurring acutely in patients who think they suffer from a demonic possession as a punishment for their acts. In these cases, symptoms are generally rapidly reversible. Lycanthropy seems to be a nonspecific manifestation of many psychiatric diseases, most commonly major depressive disorder with psychotic features. It is largely influenced by the cultural environment of the patient so that the animal species frequently represents the patient's delusional representation of evil. Lycanthropy could be considered a culture-bound syndrome that occurs in association with Axis I, DSM-IV psychiatric pathology.