Classification criteria currently exist for most of the rheumatic diseases. Different criteria sets have also been proposed in the past for Sjögren's syndrome (SS), but none of these has been validated and no single one is in general use by the entire scientific community. Between 1988 and 1996 the European Study Group for the Classification Criteria for SS performed a multicenter study in which a new classification criteria set for this disease was defined and then validated. This European set of classification criteria for SS is rapidly becoming the most widely accepted procedure to classify patients with the primary and secondary variants of the syndrome.