Obstructive sleep apnea syndrome (OSAS) and Laryngopharyngeal reflux disease (LPR) are both common health problems causing severe morbidity. Since they have similar risk factors, the prevalence of LPR among patients with OSAS is higher compared with general population. However, there exist only a few studies showing the potential causal relation between LPR and OSAS. The aim of this study was to evaluate the coexistence between OSAS and LPR and to determine whether the therapy of OSAS alters LPR parameters and vice versa. In this study, 44 patients underwent double probed 24 h pH monitoring simultaneously with polysomnography due to the complaints of obstructive sleep apnea and reflux. Twenty of those 44 patients were diagnosed with both OSAS and LPR. Among those patients, 10 patients with mild to moderate OSAS were given only LPR treatment for 3 months. The remaining 10 patients who had severe OSAS underwent CPAP treatment for 3 months. After the end of treatment, all patients were reevaluated with double probed 24 h pH monitoring simultaneously with PSG. Moreover, the patients were evaluated subjectively by Epworth Sleepiness Scale (ESS), snoring Visual Analogue Scale (VAS), Reflux Symptom Index (RSI), and Reflux Finding Score (RFS). The results of this study revealed that OSAS and LPR coexist frequently. LPR treatment did not improve the polysomnographic parameters, but significantly reduced ESS and snoring VAS (p = 0.02 and p = 0.007, respectively). Although the CPAP treatment significantly improved subjective parameters of reflux, such as RSI and RFS (p = 0.016 for both), there was no significant improvement in objective parameters of 24-h pH monitoring. We concluded that since there is a high frequency of coexistence between LPR and OSAS, all patients with OSAS should also be queried for LPR symptoms. In addition, more in-depth and comprehensive research is required to elucidate the association between OSAS and LPR.