Patients with known or suspected SLE will be evaluated in either the outpatient or inpatient research ward of the Clinical Center as indicated. Patients will not be selected based on age, race or gender. However, due to the nature of the disease, the patient population will not be expected to be evenly distributed, since SLE is predominantly a disease of young females, with increased prevalence in select racial groups, particularly African Americans and Hispanics. First and second-degree relatives of the patient may be recruited in the study for genetic analysis. We will ask for the patient s permission to contact his/her relatives, as described in details in Section IV.H.