Hallucinations that involve any of the sensory modalities may accompany a number of functional and organic conditions. Although characteristics of the hallucinations are not specific, they are characteristic and suggestive of specific disorders. Appropriate evaluation and treatment require consideration of the past psychiatric, neurologic, and medical history; assessment of accompanying psychiatric and neurologic signs and symptoms; and degree of response to conventional therapy. Any patient with hallucinations of recent onset or presenting a significant change in the nature of prior hallucinations, particularly when the patient does not respond to conventional therapy, deserves an evaluation to rule out treatable organic factors.