Purpose: Medical errors is a major health-safety issue in many hospitals; however, many of those errors are went underreported. Willingness of nurses to report the errors accurately is a key role in overcoming the underreporting issue. Therefore, this study determined the frequency of errors, error underreporting in Omani hospitals, and nurses' perceptions of the adequacy of the processes of error reporting and the most common errors, as well as the beliefs about reasons for underreporting. Method: The study used a descriptive cross-sectional design. Data were collected from 31 units in 11 Omani hospitals from July 2016 to July 2017 using incident reports and surveys completed by 562 nurses. Nurses were asked about reasons for underreporting, common errors on their patient units, and the adequacy of error reporting processes. Data were analyzed using SPSS version 24. Results: The rate of errors determined by incident reports was compared to the rate provided by the Institute of Health Improvement using its trigger tool. In comparison to the predicted error rate of .40 identified by the trigger tool, the rate of errors across all units was .0164. There was a significant difference in reported and predicted rates (z = 4.36, p < .001). All units (31) had significantly lower than predicted error rates, indicating underreporting. Despite the belief that the error reporting processes were adequate, most nurses identified fear of punishment as a common reason for underreporting. Conclusion: Fear was identified as a common cause of underreporting; therefore, it is necessary to implement a culture of safety to address underreporting, inaccuracy in rates of medical errors, and patient safety.