The authors reviewed 21 studies dealing with the rate of diagnosed and undiagnosed physical illnesses in the psychiatric patient population. These studies performed by different authors in variable clinical settings with diverse methodology in different locations over a period of 45 years yielded a close concordance. Approximately half of the patients (50.1%) suffered from significant physical illnesses, of these 58.2% were previously undiagnosed. A substantial portion of the physical illnesses (27.1%) produced symptoms showing direct relation to the psychopathology of the patient. These numbers are quite close to those found by authors in earlier research.