Background: The retained surgical items (RSIs) represent serious medical errors. The presence of an external item in the surgical site, particularly in body cavities, including the chest, abdomen, and pelvis, can cause life-threatening and financial risks for both patients and surgeons, although it is not a common occurrence. Therefore, to provide the perspective of operating room nurses for preventing counting errors during surgery, it is essential to investigate factors associated with counting errors from their point of view in this area. The purpose of the study was to investigate factors affecting the incidence of counting errors from the point of view of operating room nurses. Methods: This qualitative study was conducted based on the content analysis approach, with a focus on the research objectives, in hospitals affiliated with Jahrom University of Medical Sciences. The participants were 10 operating room nurses selected through the snowball sampling method as non-probability sampling. Semi-structured interviews were used to collect the data. Sampling was started as purposive sampling and continued until reaching data saturation. Data were analyzed using the Graneheim and Lundman method approach. Results: Based on the data analysis, three main categories were identified regarding the causes of counting errors in the operating room, including factors related to the operating room nurses, factors related to the surgical conditions, and factors related to the organization. Conclusion: Factors contributing to counting errors in surgery were wide and multifactorial. Identifying factors contributing to errors is the first step to prevent errors. Considering individual and organizational factors effective in the occurrence of counting errors, as well as the special conditions of each surgery, effective measures can be taken to reduce the counting error.