OBJECTIVE Sleep hygiene-related conditions are factors that affect the symptoms experienced by patients with obstructive sleep apnea (OSA). However, very few studies have investigated the association between sleep hygiene and sleep symptoms, especially in patients with mild or moderate OSA. This study evaluated the relationship between factors related to sleep hygiene and clinical symptoms in patients with mild to moderate OSA. METHODS One hundred and seventy-four patients who visited the Sleep Breathing Disorder Center at a tertiary academic center to evaluate suspected OSA were included. All patients underwent standard polysomnography (PSG) and the Epworth sleepiness scale (ESS) and questionnaires related to daytime and nighttime symptoms and sleep hygiene. Medical records were reviewed for demographic, clinical, and PSG parameters. Correlation analysis between sleep hygiene-related conditions and clinical symptoms in patients with mild to moderate OSA was performed. RESULTS The correlation analysis between the nine categories of sleep hygiene and the three categories of clinical symptoms showed that, in the case of inadequate temperature and humidity conditions, the three categories of clinical symptoms were more severe (daytime symptoms r=0.382, nighttime symptoms r=0.568, ESS score r=0.321). Drinking alcohol before sleep (daytime symptoms r=0.457, nighttime symptoms r=0.649, ESS score r=0.301) and emotional excitement or arousal (daytime symptoms r=0.378, nighttime symptoms r=0.545, ESS score r=0.341) were correlated with greater severity of each of the clinical symptoms (p<0.05). CONCLUSIONS Among the factors of sleep hygiene-related conditions, inadequate temperature and humidity, drinking alcohol before sleep, and emotional excitement or arousal were associated with symptoms of mild to moderate OSA. This study supports the hypothesis that patients with mild to moderate OSA can experience symptom relief if they are trained to correct lifestyle habits to maintain adequate sleep hygiene-related conditions.