The optimal outcome measures to be employed in clinical trials of systemic lupus erythematosus (SLE) have yet to be determined. Useful instruments should assess disease outcome in terms of all organ system involvement, as well as measures important to the patient. This article reviews those outcome measures that have been utilized in cohort studies in SLE, as well as their limited use in randomized clinical trials (RCT). Six disease activity measures have been developed: British Isles Lupus Assessment Group Scale (BILAG), European Consensus Lupus Activity Measure (ECLAM), Lupus Activity Index (LAI), National Institutes of Health SLE Index Score (SIS), Systemic Lupus Activity Measure (SLAM), and Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). They have been validated in cohort studies as reflecting change in disease activity, and against each other. RCT utilizing SLAM, SLEDAI, BILAG, ECLAM, SIS, SLAM, SLEDAI are ongoing. It is recommended that the disease activity index of choice be selected; but simultaneous computer generation of multiple indices will facilitate comparisons across therapeutic interventions. A damage index has been developed and validated as the Systemic Lupus International Cooperating Clinics (SLICC)/American College of Rheumatology (ACR) Damage Index or SDI. In several cohort studies it has been shown sensitive to change over time, and to reflect cumulative disease activity. There is no health status or disability instrument specific to SLE. The Medical Outcomes Survey (SF-20) captures health status/health related quality of life (HRQOL) better than the Health Assessment Questionnaire (HAQ) in patients with SLE, but does not adequately reflect fatigue. The SF-36 does assess fatigue, and correlates closely with the SF-20. These data indicate that any individual measure of clinical response to a therapeutic intervention in SLE may reflect only a portion of what might be termed the "true outcome." Based on this work, the way is now paved to attempt to develop consensus on the important domains to be measured in clinical trials in SLE, the most appropriate instruments to use and the minimal clinically important differences in their results.