P.H., E.C., and J.D. were full-time employees of, and own stock options in, Actelion Pharmaceuticals Ltd. All the other authors were investigators of the study, and payments were received either by them or by their institutions from Actelion Pharmaceuticals for performing the study and for travel and/or accommodation expenses for investigator meetings related to the study. The Siesta Group Schlafanalyse, Vienna, Austria, was paid by Actelion Pharmaceuticals for data analysis. The following authors report disclosures for activities unrelated to the submitted work: G.D. is the chief executive officer of the Siesta Group Schlafanalyse and is also employed by Philips Respironics; he owns stock options in the Siesta Group and has been paid for his expert testimony by the Gerson Lehrmann Group. G.D.'s institution has received grants from Philips Respironics, and the Siesta Group provides analysis services to several pharmaceutical companies. H. Beneš. has received honoraria from GSK, Boehringer Ingelheim, Cephalon, and UCB for educational lectures and advisory board meetings. T.P. has received financial support from several pharmaceutical companies for attending conferences and advisory board meetings, and his institution has received grants from the European Union and German National Funds. H.D.-H. has received consultancy fees from PAREXEL International and refund of travel expenses incurred for activities supported by GSK, MSD, Sanofi-Synthelabo, and UCB; her institution has received grants from Actelion Pharmaceuticals, GSK, MSD, Bioprojet, and PAREXEL International. G.P. has received payments from Actelion Pharmaceuticals for expenses relating to his position as a steering committee member of a separate study. B.S. has received research support from Abiogen Pharma, Actelion Pharmaceuticals, AstraZeneca, Cephalon, GlaxoSmithKline, Sanofi-Aventis, Schwarz Pharma, Servier, and Takeda. He has received honoraria (not exceeding US$10,000/year) for serving on scientific advisory boards of Nycomed, Servier, Takeda, UCB, and Sanofi-Aventis; for being a consultant for Merck and Xenoport; and for being a speaker for AstraZeneca, Cephalon, Ixico, Janssen, and Lundbeck. He is a shareholder of the Siesta Group Schlafanalyse. O.P. has received consultancy fees from Orion Pharma, MSD, Pfizer, and Actelion Pharmaceuticals, and payment from Boehringer Ingelheim, Pfizer, GSK, AstraZeneca, and Maribo Medical for lectures; he owns stocks in Unesta, which provides services for several pharmaceutical companies. M.P. has received consultancy fees from Cephalon, Leiras-Nycomed, Sanofi-Aventis, Servier, and UCB, and payment from Boehringer Ingelheim, GSK, Leiras, Servier, and UCB for lectures; his institution has received grants from the Academy of Finland and the Parkinson Foundation. C.L.B. has received payments from UCB, Pfizer, Boehringer Ingelheim, Bioprojet, Lundbeck, and Actelion Pharmaceuticals for advisory board membership, and from UCB, Pfizer, Lundbeck, Bioprojet, Boehringer Ingelheim, and Novartis for lectures; his institution has received grants from UCB, Pfizer, ResMed, and Respironics, and payment from Pfizer for the development of educational presentations. B.H. has received consultancy fees from UCB, Boehringer Ingelheim, GSK, Pfizer, and Jazz Pharmaceuticals; payments from UCB, Boehringer Ingelheim, GSK, Cephalon, and Sanofi for lectures; and royalties from CUP. Her institution has received grants from UCB. Y.P. has received payments from ResMed, Roche, and AstraZeneca for lectures, and his institution has received grants from the Swedish Heart and Lung Foundation and other national and local foundations as well as from ResMed, ResMed Foundation, Pfizer, Boehringer Ingelheim, and Actelion Pharmaceuticals. U.-M.H. has received payment for serving on advisory boards of Eli Lilly, Bristol-Myers Squibb, and Pfizer. G.H. has received consultancy fees, payments for advisory board membership and participation in speaker boards, and research funding from Actelion Pharmaceuticals, AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Cephalon, Daimler Benz, Eli Lilly, EuMeCom, Essex Pharma, Gerson Lerman Group Council of Healthcare Advisors, GSK, Janssen-Cilag, Lundbeck, McKinsey, MedaCorp, Merck, Network of Advisors, Novartis, Organon, Pfizer, Sanofi-Aventis, Schering-Plough, Sepracor, Takeda, Transcept Pharmaceuticals, UCB, Volkswagen, Weinmann, and Wyeth. D.K., J.Z., S.B., I.O.E., E.H.-T., and H. Bengtsson have no financial disclosures or potential conflicts of interest to report. M.J.B. is deceased and therefore no disclosures are reported for this author.