Purpose: The aim of this study was to investigate whether wearing complete dentures during sleep can improve the apnea-hypopnea index (AHI). Materials and Methods: A total of 34 edentulous patients (16 men and 18 women, mean age: 72.5 ± 8.8 years) completed the study. Portable sleep recording was performed for two nights in patients' homes. All patients wore complete dentures one night and slept without dentures the other night. Information about medical history and denture use was obtained for all patients. The occurrence of obstructive sleep apnea syndrome (OSAS) was calculated in edentulous patients, and the effect that wearing complete dentures during sleep had on the AHI was evaluated. Results: Twenty-seven of the 34 patients suffered from OSAS with an AHI >= 5. The mean AHI in patients sleeping with dentures was lower than that of those without dentures (13.3 ± 10.0 versus 17.7 ± 14.6, P = .022). Nineteen of these 27 patients showed a decrease in AHI while eight showed an AHI increase, of whom four showed increases of more than 5 points when wearing dentures during sleep. Conclusions: Wearing complete dentures during sleep improves the AHI of most edentulous OSAS patients. In contrast, some patients suffer from AHI increases due to the use of complete dentures. Also in some patients, any significant change in AHI associated with the usage of complete dentures went unnoticed. Thus, careful attention should be given when complete dentures are recommended for edentulous OSAS patients.