Of a consecutive series of 117 psychiatric inpatients with hallucinations, all had primary affective disorder, schizophrenia, alcoholism, organic brain syndromes, or hysteria. Hallucinations were found to be nonspecific. Most patients who had hallucinations involving one sensory modality had experienced in the past hallucinations involving other sensory modalities. The hallucinations accompanying acute schizophrenia more closely resembled those seen in affective disorder than in chronic schizophrenia, but no type of hallucination was diagnostic in the sense of occurring significantly more often in one illness than in another. Auditory hallucinations occurred almost as often in affective disorder as in schizophrenia; visual hallucinations were common in all five disorders; and derogatory voices, widely believed to signify depression, occurred most often in schizophrenia.