We investigated the frequency of undiagnosed sleep apnea in patients scheduled for elective total joint arthroplasty. Two hundred fifty-four patients were assessed between September 1999 and May 2001. At intake, patients were given a standard systems review with the addition of targeted questions about sleep apnea. Ten patients reported symptoms consistent with undiagnosed obstructive sleep apnea (OSA). The identification of undiagnosed OSA is an issue for orthopedic practice because many patients referred to an arthroplasty service for hip and/or knee surgeries are obese. A few screening questions, readily incorporated into the preoperative assessment, may prevent perioperative complications such as postextubation airway obstruction, negative pressure pulmonary edema, or opioid-induced airway obstruction.