Objective: The aim of this study was to investigate the characteristics of patients whose identities are unknown at presentation to psychiatric services.

Method: We retrospectively reviewed 12 years of presentations to an emergency psychiatric unit and identified 37 anonymous presentations in that period. Cases were assessed with regard to demographic data, legal status, reasons for presentation, putative diagnosis at presentation, eventual documented (ICD-9) diagnosis, previous history, duration of anonymity, method of identification and re-occurrence.

Results: 0.6% of all patients who presented during the study period were unidentified for at least 24 hours. Patients were young (mean age 33.6 years). Over half were of foreign nationality (53%). The majority were suffering from major psychotic illnesses (86%). When compared with all admissions during the study period, schizophrenia and drug-induced psychoses were significantly more common in the group unidentified at presentation. Malingering, organic psychiatric disorders and dissociative states were not commonly encountered underlying diagnoses. All of our patients were subsequently identified. Successful identification methods included self admission, careful examination of personal belongings, careful history taking, liaison with police and recognition by staff. Patients frequently had a previous psychiatric history (91%). Recurrence was uncommon.

Conclusion: The anonymous presentation represents a unique challenge to the investigative skills of the psychiatrist. The application of basic strategies enables the successful identification of the majority of cases.