Background: The aims of the survey was to analyze the musculoskeletal system load during work performed by operating room nurses, and to identify the most loading activities along with their causes. Material and Methods: The observation of work process and the Ovako Working posture Analysing System (OWAS) method for analyzing and evaluating work postures were used as major tools of this survey. Altogether 170 observations of work process were made and also seven basic work activities and 101 320 work postures were selected. Results and Conclusions: The results of the survey show: a) average proportion of time spent by nurses on individual tasks during the shift were: preparation for operative procedure - 16%, instrumentation nurse tasks - 16%, circulating nurse tasks - 13%, cleaning after operative procedure - 4%, cleaning and preparation of surgical instruments - 4%, breaks at work - 43% and other tasks - 4%; b) average proportion of time spent by nurses in OWAS posture categories were: category 1 - 89%, category 2 - 10%, category 3 and 4 - 1%. The collected data revealed that the main causes of the musculoskeletal system load in all tasks were: time spent by nurses on awkward postures during the shift (inability to change postures), awkward postures with a hard load (manual lifting or transporting the equipment, more than 10 kg and also above 20 kg). It should be emphasized that the identified causes of loading activities resulted from poor work organization and technical working conditions. Med Pr 2009;60(3):187-195