This multi-centre study assessed operating room (OR) staff compliance with clothing regulations and traffic flow during surgical procedures. Of 1615 surgical attires audited, 56% respected the eight clothing measures. Lack of compliance was mainly due to inappropriate wearing of jewellery (26%) and head coverage (25%). In 212 procedures observed, a median of five people [interquartile range (IQR) 4–6] were present at the time of incision. The median frequency of entries to/exits from the OR was 10.6/h (IQR 6–29) (range 0–93). Reasons for entries to/exits from the OR were mainly to obtain materials required in the OR (N=364, 44.5%). ORs with low compliance with clothing regulations tended to have higher traffic flows, although the difference was not significant (P=0.12).