STUDY OBJECTIVES:To determine the total number of active sleep laboratories in the United States and the number of polysomnograms conducted on a yearly basis in these laboratories. METHODS:All members of the AASM and all AASM accredited sleep laboratory directors received a questionnaire addressing their laboratory and its volume. In three states, multiple telephone calls to AASM members were used to correctly identify the absolute number of labs and their PSG volume in those states. Extrapolating from the number of labs studies identified per questionnaire relative to the correct number (per calls) in those states and, then applying this ratio to the entire US, the total number of labs and studies was determined. RESULTS:Our data suggests that there are, in the year 2001, 1,292 sleep laboratories conducting 1,165,135 polysomnograms per year. This comes to 427 PSG's/year per 100,000 population in the United States. CONCLUSIONS:These data suggest that there are a relatively large number of sleep laboratories in the US conducting a substantial number of PSG's. However, there was considerable variability in this volume between states that did not relate to known markers of healthcare utilization. These numbers have likely increased since 2001.