Work in health care units is associated with considerable physical strain and many musculoskeletal complaints. Most investigations have concentrated on the work of general hospital nurses; little is known about the physical stress load on other health care workers. We therefore carried out an ergonomic study amongst operating room staff in order to (i) determine the work (posture) stress load on this particular group of health care workers and the effect of static posture on this stress, (ii) identify activities involving poor work postures, and (iii) determine differences between specialties in regard to work posture stress load. The work postures and related work activities of four different groups of staff in operating rooms (surgeons, assistant anaesthesists, instrumentation nurses and circulating nurses) were recorded and evaluated using the specified Ovako Working posture Analysing System (OWAS). Observation during the course of 18 daily surgical programmes (total number of observations: 3714) in the specialties general surgery and ear-nose-throat (ENT) surgery revealed that the work-load according to OWAS for circulating nurses and assistant anaesthesists was not harmful. Some work postures seen among instrumentation nurses and surgeons, however, need improvement. The work posture stress load in these groups is mainly due to the high prevalence of static work postures during the activities "surgery" (surgeons) and "assisting surgery" (instrumentation nurses). Significant differences in ergonomic stress load were observed between general surgeons and ENT surgeons. This survey in operating theatres relates work postures to basic activities and can be used as a starting point from which to improve work conditions in order to reduce or eliminate physical complaints among operating room staff.