Both voluntary in-hospital reporting and mandatory national-level reporting systems for patient safety issues need to work well to develop a patient safety learning system that is effective in preventing the recurrence of adverse events. Some of the hospital systems and activities may increase voluntary in-hospital reporting and mandatory national-level reporting. This study aimed to identify the hospital systems and activities that increase voluntary in-hospital reporting and mandatory national-level reporting for patient safety issues. An anonymous mail survey of hospitals in Japan was conducted in 2017. The hospitals were selected by stratified random sampling according to number of beds. The survey examined the annual number of reported events in the voluntary in-hospital reporting system for patient safety and experience of reporting unexpected patient deaths possibly due to medical interventions to the mandatory national-level reporting system in the last 2 years. The relationship of the answer to the questions with the patient safety management systems and activities at each hospital was analyzed. The response rate was 18.8% (603/3,215). The number of in-hospital reports per bed was positively related to identifying events by referring complaints or questions of patients or family members, using root cause analysis for analyzing reported events, and developing manuals or case studies based on reported events, and negatively related to the unification and standardization of medical devices and equipment. The experience with mandatory national-level reporting of serious adverse events was positively related to identifying problematic cases by a person in charge of patient safety management from the in-hospital reporting system of complications and accidental symptoms. Enhanced feedback for reporters may promote voluntary in-hospital reporting of minor cases with low litigation risks. Developing an in-hospital mechanism that examines all serious complications and accidental symptoms may promote mandatory national-level reporting of serious adverse events with high litigation risks.