ABSTRACTThe purpose of this study was to measure the reliability of scoring all‐night EEG sleep records. To determine the amount of inter‐rater agreement of scoring EEG sleep stages, 28 raters from 14 different sleep laboratories scored the same 398 minute sleep record.Statistical analyses showed varying amounts of inter‐rater agreement across sleep stages with St. REM showing the highest reliability and delta stages the least inter‐rater agreement. A comparison of raters with High, Medium, and Low experience revealed lower within‐group variability for Stages 1, 2, 3, and 4 for the more experienced raters.It was concluded that increased reliability and comparability of results could be obtained readily by increased standardization of recording techniques and scoring