Various studies across the world suggest that, on average, one in every ten patients admitted to hospital suffer harm from tests or treatments intended to help them. Such accidental injury is more likely to happen in some parts of the hospital than others. About 7 million operations are performed annually on patients admitted to hospitals in England and Wales, 1 so a large number of patients are exposed to errors and deviations from recommended practice, and some will suffer injury as a result. This paper describes some patient safety problems that occur in operating theatres and suggests ways to promote safety.