The goal of the 'Outcome Measures in Rheumatology' (OMERACT) process is to select domains and/or outcome measures for clinical trials in each defined disease category according to truth, discrimination and feasibility. OMERACT IV, held in Cancun, Mexico, April 1998, included the module 'Systemic Lupus Erythematosus (SLE)', designed to define a preliminary core set of outcome domains for randomized controlled trials and longitudinal observational studies (LOS). Although specific measures to be used in clinical trials of SLE have yet to be determined, both randomized controlled trials and longitudinal observation studies groups recommended that outcome be assessed in terms of disease activity and damage in all organ systems involved, as well as by health related quality of life, meaningful to patients, and adverse events. These recommendations were ratified by the majority of participants. In a heterogeneous patient population such as SLE, it is recognized that any individual measure of clinical response may reflect only a portion of what might be termed the 'true outcome'. A responder index could integrate such relatively independent measures of outcome into a single assessment, potentially increasing statistical power and decreasing sample size. Results from randomized controlled trials currently underway assessing these outcome domains are eagerly awaited, and are expected to rapidly advance the field.