The classification criteria for Sjögren's syndrome (SS) were developed and validated by the European Study Group on Classification Criteria for SS between 1989 and 1996. These criteria were later revised by an American-European Consensus Group to improve accuracy and clarity. The revised criteria aim to better classify patients with primary or secondary SS, define exclusion criteria, and standardize diagnosis for clinical studies. SS is an autoimmune disease characterized by lymphocytic infiltration of exocrine glands, leading to dry eyes and mouth. It can occur alone (primary SS) or in association with other autoimmune diseases (secondary SS). The diagnostic approach requires assessing ocular and salivary components and differentiating between primary and secondary forms. Previous classification criteria had limitations, including potential misclassification of patients without specific markers. The revised criteria, based on ROC curve analysis and classification tree procedures, improved sensitivity and specificity. The C* point, which excludes cases with negative serology and histopathology, was found to be more reliable for standardizing patient selection in studies. The revised criteria include specific tests for dry eye and dry mouth, modified histopathology definitions, and updated criteria for sialography and scintigraphy. Exclusion criteria were also updated, including hepatitis C virus infection, which can mimic SS. For secondary SS, the revised criteria showed better performance when including subjective symptoms. The American-European Consensus Group approved the revised criteria as the best available for SS classification, emphasizing their use in clinical and epidemiological studies. The criteria are not a definitive diagnostic tool but help standardize diagnosis in research. The study was supported by the European BIOMED Concerted Action and the Sjögren's Syndrome Foundation.The classification criteria for Sjögren's syndrome (SS) were developed and validated by the European Study Group on Classification Criteria for SS between 1989 and 1996. These criteria were later revised by an American-European Consensus Group to improve accuracy and clarity. The revised criteria aim to better classify patients with primary or secondary SS, define exclusion criteria, and standardize diagnosis for clinical studies. SS is an autoimmune disease characterized by lymphocytic infiltration of exocrine glands, leading to dry eyes and mouth. It can occur alone (primary SS) or in association with other autoimmune diseases (secondary SS). The diagnostic approach requires assessing ocular and salivary components and differentiating between primary and secondary forms. Previous classification criteria had limitations, including potential misclassification of patients without specific markers. The revised criteria, based on ROC curve analysis and classification tree procedures, improved sensitivity and specificity. The C* point, which excludes cases with negative serology and histopathology, was found to be more reliable for standardizing patient selection in studies. The revised criteria include specific tests for dry eye and dry mouth, modified histopathology definitions, and updated criteria for sialography and scintigraphy. Exclusion criteria were also updated, including hepatitis C virus infection, which can mimic SS. For secondary SS, the revised criteria showed better performance when including subjective symptoms. The American-European Consensus Group approved the revised criteria as the best available for SS classification, emphasizing their use in clinical and epidemiological studies. The criteria are not a definitive diagnostic tool but help standardize diagnosis in research. The study was supported by the European BIOMED Concerted Action and the Sjögren's Syndrome Foundation.