Primary Sjögren's syndrome seems to be the most common of the chronic systemic inflammatory connective tissue diseases, according to epidemiological investigations. Basic and clinical research, including treatment within this group, is increasing while simultaneously there is increasing confusion and uncertainty about the classification criteria for Sjögren's syndrome. Within the last three decades nine different classification criteria sets have been introduced including the recent US-European classification criteria set. The diagnostic criteria used in daily practice seem to differ even more and many forget that the function of both the lachrymal glands and the salivary glands should be diminished. Consequently many rheumatologists prefer to diagnose patients according to classification criteria. The advantages and disadvantages of the various classification criteria for primary Sjögren's syndrome are dealt with but it is stressed that the majority of these will exclude former/present smokers (from the diagnoses)--more than half of the population!