This study aims to determine whether there is an increased prevalence of obstructive lung diseases (OLDs) in patients with obstructive sleep apnea (OSA). We also determined whether among the OLD patients there is a difference in the prevalences of specific chronic disease co-morbidities between patients with and without OSA. METHODS The prevalences of COPD, asthma, and COPD combined with asthma (ICD-9 coding) were compared between 1,497 adult OSA patients and 1,489 control patients, who were matched for age, gender, geographic location, and primary care physician. The prevalences of specific co-morbidities were measured in the OLD groups between patients with OSA and the matched control group. RESULTS COPD, asthma, and COPD combined with asthma were found to be more prevalent among OSA patients compared to the matched controls. Prevalences among patients with and without OSA, respectively, were COPD-7.6 and 3.7 % (P<0.0001), asthma-10.4 and 5.1 % (P<0.0001), COPD plus asthma-3.3 and 0.9 % (P<0.0001). The Charlson Comorbidity Index was greater for OSA patients (2.3 ± 0.2) than for controls (1.9 ± 1.8; P<0.0001). These trends held for all severity ranges of OSA. Patients with OSA and COPD were characterized by more severe hypoxia at night compared with the OSA patients without OLD. CONCLUSIONS OSA was associated with an increased prevalence of OLDs.