Introduction: The European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria for systemic lupus erythematosus (SLE) established a new criteria system with antinuclear antibodies (ANA) as an entry criterion, domains, and weighted criteria. In the validation cohort, specificity and sensitivity each matched the best performance of the previous criteria sets. Areas covered: Groups worldwide have externally validated the EULAR/ACR SLE classification criteria. Studies on the classification criteria were searched on PubMed and analyzed for their estimates of criteria performance. These were combined with new insights from the EULAR/ACR criteria project to understand any differences in assessments. Expert opinion: Overall, external validation supports the concepts and performance of the new SLE criteria. Variation in specificity in part appears to be related to incomplete application of the attribution rule of the criteria, under which items should only be counted for SLE if there were no more likely alternative explanation. Scientific uncertainty, and a lack of worldwide consensus, on the borderline between disease entities, e.g. between SLE and isolated cutaneous lupus erythematosus (CLE), also affected variation in estimates. For sensitivity, the performance of tests for ANA is critical.