The assessment of disease activity in systemic lupus erythematosus (SLE) is a task faced by clinicians in every day care, but it is also required for clinical research and in randomised controlled trials. It is crucial to distinguish disease activity from infection, chronic damage and co-morbid disease. Over the past 20 years, many indices have been developed to objectively measure lupus disease activity and several of these have been validated. The most widely used indices are the British Isles Lupus Assessment Group (BILAG) index, the European Consensus Lupus Activity Measurement (ECLAM), the Systemic Lupus Activity Measure (SLAM), the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) and the Lupus Activity Index (LAI). All these indices have been validated and have excellent reliability, validity and responsiveness to change. In addition to the assessment of disease activity, the evaluation of damage using the validated SLICC/ACR damage index and health-related quality of life is advised for clinical research.