Regarding the issue of variability, as long as we continue to use a sleep-disordered breathing index to make this diagnosis, there will always be significant variability, whether we are looking at standard polysomnography or portable monitoring. Polysomnography has the significant advantage of the measurement of sleep and its architecture, and will always be better than portable monitoring because of the multiplicity of channels and the attendance by a technician. Few data are available regarding the use of portable monitoring in patients other than middle-aged white men. An evidence review,3a study on practice parameters,4 and, more recently, a panel from CMS, concluded that there is not enough support in the literature to allow portable monitoring (specifically, unattended level 3 systems) to be utilized indiscriminately for the diagnosis of sleep apnea. Portable monitoring will be acceptable, in my eyes, when these devices have been thoroughly validated and when the populations in which sleep apnea can be accurately diagnosed using these devices have been defined.