 The study hypothesis is that the prevalence of obstructive sleep apnea in patients presenting for total knee or total hip arthroplasty is higher than generally suspected. The study will include just one arm and results will be compared to a literature control group. Patients refered for preoperative evaluation will be screened using a standard questionnaire. Those at high risk of obstructive sleep apnea will then undergo a formal overnight sleep study polysomnography. 