A group of 20 patients with mixed connective tissue disease, followed for up to five years, was found to have a 55 per cent incidence of neuropsychiatric problems. An aseptic meningitis-like syndrome was the most common presentation and was rapidly responsive to corticosteroid therapy. Other findings were psychosis, convulsions, peripheral neuropathy, trigeminal neuropathy and cerebellar ataxia. An abnormal cerebrospinal fluid was found in five patients; mild pleocytosis, an increased protein content and a first phase colloidal gold curve were the main abnormalities. These neuropsychiatric problems have not been a cause of mortality in this group of patients with mixed connective tissue disease.