The definitions of respiratory events and recommendations concerning monitoring technology will continue to evolve as more knowledge is gained about the effect of using different definitions or technology on outcomes. Improved ability to predict patients who will improve symptomatically with treatment (especially in patients with "milder" obstructive sleep apnea) is clearly needed. It is hoped that this document is simply a starting point of a new process to provide a flexible and evolving set of respiratory definitions. The recommendations in this document are based predominantly on consensus. The task force attempted to carefully weigh the current evidence as well as to respond to concerns raised by the sleep community about the recommendations in the 2007 scoring manual. Many areas of uncertainty remain. No set of definitions can completely cover the wide variety of respiratory events encountered by clinicians. There is no substitute for clinical correlation of PSG findings with the clinical symptoms of the patient being evaluated.