The prevalence of GER disease (GERD) is as high as 20% in the Western world with up to 10% of people reporting symptoms of nocturnal reflux exclusively. Obstructive sleep apnea (OSA) has estimation of affection in 4% of men and 2% of women in USA and the rates continue to increase. The aim of this work is to determine the frequency of OSA in patients with GERD studying the association between GERD and OSA, and to evaluate the effect of nCPAP on GERD symptoms. Subjects and methodsOne hundred and thirty-six subjects suspected to have GERD were subjected to the following: (1) thorough medical history stressing on OSA symptoms, (2) clinical examination, (3) chest X-ray, (4) routine investigations (complete blood count, liver and kidney functions, fasting blood sugar), (5) upper GIT endoscopy, (6) Epworth questionnaire, and (7) polysomnography for patients who were suspected to have sleep-disordered breathing upon Epworth questionnaire (109 patients). The patients were classified according to endoscopic findings into 2 groups: Group I: erosive reflux disease (ERD) group which included 65 patients; 42 males and 23 females with a mean age of 55.3±7.2 and Group II: non-erosive reflux disease (NERD) group which included 71 patients; 49 males and 22 females with a mean age of 53.8±6.8. Nasal CPAP therapy was prescribed for all OSA patients (41 patients diagnosed by polysomnography) according to the clinical protocol then they were further recruited for post nCPAP therapy assessment. All the following parameters were measured at time of recruitment and 1week later after initiation of nCPAP: BMI, pulmonary function tests: FEV1% and FVC%, sleep characteristics: AHI (event/hour slept), arousal index (event/hour slept), minimum SpO2 (%), SpO2 (%), total sleep time (min), sleep efficiency index (%) and GER symptoms including nocturnal GER (nGER). ResultsThere was a statistically significant high frequency of OSA among NERD patients than that among ERD ones. Also there was a statistically highly significant increase in apnea/hypopnea index (AHI) (event/hour) and arousal index (AI) (event/hour) in NERD group than that in ERD one. A statistically significant increase in total sleep time (min) and Epworth sleepiness scale score was found in NERD group when compared to ERD one. There were statistically highly significant decreased percentages of OSA patients who had any nocturnal symptoms and frequent nocturnal symptoms after use of nCPAP and also a statistically highly significant decrease in GERD score in OSA patients after nCPAP therapy. Conclusion(1) A high risk for OSA development is more frequent in GERD patients especially NERD ones and who experience nighttime symptoms, (2) there is a mutual relationship between OSA and GERD reinforcing each other, and (3) CPAP therapy has a good role in the treatment of both OSA and GERD symptoms.