In this review we describe an international project, conducted by the Paediatric Rheumatology International Trials Organization (PRINTO) that was aimed to identify, validate and promulgate core sets of measures and a definition of improvement for the evaluation of response to therapy in clinical trials and in daily clinical practice in patients with juvenile systemic lupus erythematosus (JSLE). The following clinical measures were included in the PRINTO core set of outcome measure for the evaluation of response to therapy: 1) physician's global assessment of disease activity; 2) global disease activity measure; 3) 24-hour proteinuria; 4) parent's global assessment of the overall patient's well-being; 5) health-related quality of life assessment. The measures included in the core set were found to be feasible and not redundant, to have good construct validity, discriminative ability, internal consistency, with fair responsiveness to clinically important change in disease activity, and to be associated strongly with treatment outcome. In order to be classified as responder to a given treatment, a patient should demonstrate at least 50% improvement from baseline in any two of the five core set measures with no more than one of the remaining worsening by more than 30%. This definition is now known as the 'PRINTO/American College of Rheumatology (ACR) provisional criteria for JSLE'. The proposed core set and definition of improvement incorporate clinically meaningful change in a composite endpoint for the evaluation of global response to therapy in JSLE. The definition is now proposed for use in JSLE clinical trials, and may help physicians to decide if a child with SLE has responded adequately to therapy.