Objective. To validate and promulgate a core set of outcome measures for the evaluation of response to treatment in patients with juvenile systemic lupus erythematosus (SLE). Methods. In 2001, a preliminary consensus-derived core set of measures for evaluating the response to therapy in juvenile SLE was established. In the present study, the core set was validated through an evidence-based, large-scale data collection process that led to the enrollment of 557 patients from 39 different countries. Consecutive patients with active disease were assessed at baseline and after 6 months. The validation procedures included assessment of feasibility, responsiveness, discriminant and construct ability, agreement in the evaluation of response to therapy between physicians and parents, redundancy, internal consistency, and ability to predict a therapeutic response. Results. The following clinical measures were found to be feasible and to have good construct validity, discriminative ability, and internal consistency; furthermore, they were not redundant, proved responsive to clinically important changes in disease activity, and were associated strongly with treatment outcome and thus were included in the final core set: 1) physician's global assessment of disease activity, 2) global disease activity measure, 3) 24-hour proteinuria, 4) parent's global assessment of the patient's overall well-being, and 5) health-related quality of life assessment. Conclusion. The members of PRINTO propose a core set of criteria for the evaluation of response to therapy that is scientifically and clinically relevant and statistically validated. The core set will help standardize the conduct and reporting of clinical trials and assist practitioners in deciding whether a patient with juvenile SLE has responded adequately to therapy.