To describe the characteristics of xerostomia (dry mouth) in the population with sleep apnea-hypopnea syndrome (SAHS) and contrast its prevalence versus that found in healthy subjects, and to compare the frequency of xerostomia in SAHS patients with and without continuous positive airway pressure (CPAP) treatment. A prospective comparative study was made between adults recently diagnosed with SAHS in a public hospital (n=60) and healthy individuals (n=54). The presence of xerostomia was assessed on waking up and during the day, using a frequency scale from 0 (?never?) to 3 (?always?). The prevalence of xerostomia on waking up in the SAHS group was 45%, versus 20.4% among the controls. During the rest of the day the prevalence of the symptom decreased in both the SAHS group (21.7%) and among the controls (9.3%). Multiple binary logistic regression analysis found body mass index (BMI) to be correlated to the association SAHS-xerostomia on waking up (p=0.007). Patients with moderate SAHS had a greater frequency of xerostomia than those with mild SAHS (p=0.022). The frequency of xerostomia on waking up was significantly greater in patients using CPAP than in those without such treatment (57.1% versus 16.7%, respectively) (p=0.008). The frequency of xerostomia was greater in patients with SAHS, particularly on waking up and in those receiving CPAP. The symptom was more prevalent in individuals with moderate to severe SAHS than in those with mild SAHS, and was significantly influenced by BMI.