The purpose of the present study was to investigate the differences in salivary flow rates and dry mouth-related subjective symptoms and behaviours in patients with xerostomia according to its aetiology. One hundred and forty patients (24 men and 116 women, mean age, 58.1 +/- 13.3 years) with a chief complaint of xerostomia were included. The patients were divided into five groups; Sjögren's syndrome (n = 34), post-radiation therapy in the head and neck region (n = 16), antipsychotic medications (n = 30), systemic diseases or medications affecting salivary flow (n = 35), and unknown aetiology (n = 25). The patients were asked a standardized series of questions concerning dry mouth, and their whole salivary flow rates were measured. Patients with a history of radiation therapy displayed the most decreased values of salivary flow rates and the most severe associated symptoms and behaviours while patients with unknown aetiology displayed the least decreased values of salivary flow rates and relatively favourable symptoms and behaviours. A burning sensation in the mouth was the most prevalent in patients with systemic diseases or those who were taking medications while altered taste perception was the most prevalent in patients taking antipsychotics. In conclusion, patients with xerostomia displayed various degrees of discomfort related to the quality of life according to the aetiology of their conditions.