Obstructive sleep apnea (OSA) is a common sleep disorder affecting approximately 16% of adults (24% of men and 9% of women), and, if untreated, it can cause significant complications ( Young, 2009 ). This study evaluates 56 adult patients with Down syndrome and analyzed retrospective data to determine the: (1) prevalence of OSA, (2) severity of OSA, and (3) association between body mass index (BMI) and OSA. Of those participants that had polysomnography (PSG) testing available, 82.1% were diagnosed with OSA, divided by severity into mild (45.7%), moderate (15.2%), and severe (39.1%) levels. Because of the high prevalence of OSA among our study population, we recommend that all adults with DS be screened for OSA with PSG.