A number of recent studies have suggested that apnea and/or hypopnea episodes may be in a causal relationship with nocturnal gastroesophageal reflux (GER) episodes in obstructive sleep apnea (OSA) patients. In this study, we addressed the possible factors that may affect the occurrence of reflux events in OSA patients. For this reason, we investigated respiratory and sleep parameters in OSA patients with or without nocturnal GER episodes. Nineteen patients who were referred to the sleep laboratory for suspected sleep apnea were included in the study. All subjects underwent polysomnographic evaluation simultaneously with distal and proximal esophageal pH monitoring. During the recording period, a total of 134 reflux events, 134 from distal probes and none from proximal probes, were recorded. We divided patients into two groups: (1) nocturnal GER-positive patients ( n=8; age: 41.9+/-11.9) and (2) nocturnal GER-negative patients ( n=11; age: 45.4+/-3.3). We compared demographic, respiratory and sleep parameters between the two groups. Then we analysed the time relation between GER episodes and obstructive respiratory events. The two groups were matched by age and body mass index. Sleep and respiratory parameters were not different between the two groups. In conclusion, we suggested that age, body mass index and the severity of disease in obstructive sleep apnea patients are not effective determinants of gastroesophageal reflux. There is no sufficient evidence to accept arousals and obstructive apneas as primary causes of gastroesophageal reflux and vice versa. And finally, sleep macroorganisation has no impact on the occurrence of GER in OSAS.