A twenty-year-old white male subject without a history of psychiatric disorder developed hallucinations and paranoid symptoms following ingestion of 540 mg codeine over a period of 36 hr. The symptoms reached an intensity where hospitalization became necessary but no specific treatment was required. In less than 72 hr, the patient completely recovered from his symptoms and was subsequently discharged. In view of the available data on the neurochemical effects of opiates and non-narcotic analgesics, it was concluded that inhibition of prostaglandin biosynthesis or interference with its action might have caused the psychotic symptoms reported.