A questionnaire, tested for validity and reliability, was developed to determine the frequency and degree of depersonalization and related phenomena among an inpatient population. These data were correlated with standard psychological tests, clinical data from the treating psychiatrists, and EEG records. Results suggested that although these phenomena are present in all patients to some degree, they occur more frequently and intensely in psychotic syndromes. The commonest depersonalization experience was that of desomatization. There was no correlation with the EEG.