The authors evaluated 14 middle-aged and elderly patients with delusional disorder (DD) and 253 patients with schizophrenia (SC); all patients met DSM-III-R criteria. Because the DD patients were older and had a later age at onset of illness, a sub-sample of 50 SC patients with illness onset after age 40 was compared with the 14 DD patients on clinical and neuropsychological characteristics. The DD group had a less frequent history of past hospitalization but more severe overall psychopathologic symptoms. Level of neuropsychological impairment seemed somewhat lower in the DD group, but differences were nonsignificant because of small sample size. Diagnoses remained stable during up to 8 years' follow-up (average 4 years). These preliminary findings provide partial support to the clinical categorization of DD as a disorder distinct from SC.