Nightly nicotine withdrawal as well as other respiratory and pulmonary effects of smoking may result in sleep-disordered breathing, especially obstructive sleep apnea (OSA). We hypothesize that there is higher prevalence of smoking in patients with OSA. We also hypothesize that smoking is an independent risk factor for OSA. The aim of this study is to determine whether there is a higher prevalence of smoking in patients with OSA compared with patients who do not have OSA. To investigate this, we randomly selected a group of 108 patients who were diagnosed as having OSA, defined by an apnea-hypopnea index (AHI) of greater than 10 events per hour. We compared their smoking history with another randomly selected group of 106 patients without OSA, defined by an AHI of less than five events per hour. The prevalence of smoking in patients with OSA was found to be 35%, whereas it was only 18% in patients without OSA. Logistic regression analyses were performed to investigate the effects of smoking while adjusting for age, gender, body mass index (BMI), and number of alcoholic drinks per week. While holding fixed the BMI, gender, age, and number of alcoholic drinks per week, current smokers were found to be 2.5 times more likely to have OSA than former smokers and nonsmokers combined (odds ratio = 2.5, CI 1.3-4.7, p = 0.0049), and 2.8 times more likely to have OSA than former smokers alone (odds ratio = 2.8, CI = 1.4-5.4, p = 0.0028). Adjusted for BMI, gender, age, and number of alcoholic drinks per week, former smokers were not more likely than never smokers to have OSA (odds ratio = 1.2, CI = 0.55-2.7, p = 0.64). We conclude that cigarette smoke may be an independent risk factor for OSA in this referral population.