Background and Objective: Nocturia is one of the common causes of sleep disturbance in adults, often associated with obstructive sleep apnea (OSA). The purpose of this study was to investigate the association between nocturia and OSA, and their effects on quality of sleep in adults. Methods: This study included 107 patients who visited the urology outpatient due to lower urinary tract symptoms with or without sleep-related symptoms, assessed by using either the International Prostate Symptom Score in men or the Overactive Bladder symptoms in women. Based on these questionnaires, subjects were divided into nocturia and nocturia-free groups. In addition, all subjects completed detailed sleep questionnaires including the Global Sleep Assessment Questionnaire (GSAQ) and the Berlin Questionnaire (BQ), and provided details of voiding volumes and times. Night polysomnography (PSG) was performed in subjects with high risk of OSA, as indicated by the BQ. Results: Among the 107 study subjects (43 males, 64 females, mean age 59.2 ± 11.2 years), nocturia was present in 54.2% (58/107), self-reported sleep disturbance in 26.2% (28/107), and a high risk of OSA, with BQ > 10 points, was present in 29.0% (31/107) of subjects. The nocturia group had a significantly higher mean GSAQ total score than the nocturia-free group, indicating poorer sleep quality (p = 0.004). Nocturia was more frequent in patients with moderate or severe OSA than in patients with mild OSA (p = 0.006) based on PSG. Conclusions: Nocturia was a clinically significant sleep disturbing factor, and it was more frequent in patients with more severe OSA.