Obstructive sleep apnea (OSA) is a common chronic medical condition that results in impaired daytime functioning. While the link between OSA and cardiovascular disease is important, there has been increasing recognition of the impact of OSA on daytime functioning and experience. Better insight into illness perceptions can help better understand how to initiate and maintain treatment. Data from two OSA clinical trials were examined. The baseline Respiratory Event Index (REI) was obtained from diagnostic sleep testing. The Brief Illness Perception Questionnaire (BIPQ) assesses the cognitive and emotional representation of illness and was administered at baseline along with the Epworth Sleepiness Scale (ESS) and the Pittsburgh Sleep Quality Index (PSQI). 523 patients diagnosed with OSA were studied. The sample had a mean age of 51.1 ± 16.6, mean REI of 28.6 ± 17.9/h, and mean body mass index of 32.8 ± 15.5 kg/m^2. The mean BIPQ total score at baseline was 43.3 ± 11.3. BIPQ scores were significantly correlated with sleepiness and sleep quality but not with REI. Relative to other common chronic conditions with major comorbidities, BIPQ scores for patients with OSA were higher on consequences, identity, concern, and emotional representation dimensions. The study shows that Veterans with OSA report elevated illness perceptions across several dimensions at levels as high, or higher, than other common chronic conditions. Implications for clinical practice are that it is important to ask patients about their understanding of illness across several dimensions to appreciate better patient needs and preferences.