1. Among patients with SLE, 71 (51%) had significant neuropsychiatric problems during the course of the disease. In 52 (37%), the nervous system manifestations were secondary to SLE. 2. The most frequent manifestations were psychiatric dysfunction, seizures, long tract signs, cranial neuropathy, and peripheral neuropathy. 3. Psychiatric abnormalities secondary to SLE were characterized by organic features (present in 22 of 24) and by the association of neurologic lesions which were often diffuse or multifocal. 4. An abnormal cerebrospinal fluid was found in 32% of neuropsychiatric episodes in which specimens were obtained. The most frequently abnormal study was the electroencephalogram (71%), and the least frequent was the brain scan (8%). These studies did not correlate with specific clinical patterns. 5. In 63% of the patients, NP manifestations preceded the diagnosis of SLE or occurred within the first year of diagnosed disease, and in most episodes were associated with evidence of clinical and/or serologic activity of the underlying illness. 6. Only two clinical features showed significant and striking correlations with neuropsychiatric involvement, namely vasculitis and thrombocytopenia. The possible pathogenic implications have been discussed. 7. Only 2 of the 140 patients were felt to have steroid-induced psychoses. In approximately one-half of the NP episodes secondary to SLE, patients were receiving no corticosteriods on presentation. Of those developing while patients were on steroids, the majority occurred on low doses or after tapering from higher levels. 8. The immediate prognosis for improvement in neuropsychiatric function was good with 84% of episodes showing complete or partial resolution. Corticosteroids appeared to be of benefit in a substantial number of patients although their precise role is difficult to quantitate. 9. Five and 10 years survivals for the overall population were 94% and 82%, respectively. There were no significant differences in survival for patients with or without nervous system involvement.