Background: Incident reporting is an effective strategy used to enhance patient safety and quality improvement in healthcare. An incident is an event that could eventually result in harm to a patient. The aim of this study is to re-evaluate the importance of reporting by medical doctors to improve quality in healthcare and patient safety. Methods: We conducted a retrospective analysis of the reported incidents registered in our institutional database from April 1st 2015 to March 31st 2019, classified according to eight variables proposed by the National University Hospital Council of Japan, to determine the type of incidents and their potential harm to patients. Results: Registered reports totalled 43,775, approximately 8% of which arise annually from medical doctors in clinical departments. Incidents with higher impact on patients have significantly increased the rate of reporting by medical doctors. The most frequent types of report overall concerned medication incidents, followed by infusion lines, drainage-tube devices, cure, examination, and treatment outside the operating room. The most frequent reports by medical doctors involved operation-related incidents, followed by cure, examination, treatment outside the operation room, and medications. Conclusion: Reporting by medical doctors reflects the organizational transparency and the driving forces behind patient safety and quality improvement in healthcare. Efforts toward seamless improvement in patient safety and quality at our hospital continue apace.