Introduction: The aim of our study is to contribute to the elucidation of the nocturia mechanism in patients with Obstructive Sleep Apnea Syndrome (OSAS) by investigating the frequency of nocturia, evaluation of polysomnography parameters, and examining whether there is improvement in nocturia after Continuous Positive Airway Pressure (CPAP) treatment. Material and Method: 100 male patients were included in the study. The relationship between patients’ age, Body-Mass Index (BMI), neck circumference, CPAP values, comorbidities and nocturia were examined. Patients with nocturia were re-evaluated for nocturia at 12 weeks after CPAP. Results: A total of 100 male patients with a mean age of 49 (min 31-max 76) were included in the study. Nocturia was present in 41 of the patients included in the study. When we grouped the patients as BMI > 35 and ? 35 and as > 43 cm and ? 43 cm in neck circumferences, there was a significant difference in the presence of nocturia in those with BMI > 35 and neck circumferences > 43 cm. Conclusion: It was observed that the frequency of nocturia was 41% in our study group, and there was a significant relationship between BMI and neck circumference measurements and nocturia. There was a significant difference between the number of nighttime urination before and after CPAP. It is important to consider OSAS in the differential diagnosis, especially in patients who do not have a history of uncontrolled Diaebetes Mellitus (DM), Benign Prostatic Hyperplasia (BPH), HF, diuretic use for the etiology of nocturia, since OSAS treatment improved nocturia in our patients.