Approximately 20 years have passed since hospital information systems (HISs) featuring full-scale electronic medical records were first implemented in Japan. Patient safety is one of the most important of the several "safety" roles that HISs are expected to fulfill. However, insufficient research has analyzed the contribution of HISs to patient safety. This paper reviews the history of HISs in connection with patient safety in Japan and discusses the future of the patient safety function of HISs in a favorable environment for digitization. A review on the history of HISs with functions that contribute to patient safety was conducted, analyzing evidence from reports published by the Japanese government and papers on patient safety and HISs published in various countries. Patient safety has become a concern, and initiatives to promote patient safety have progressed simultaneously with the spread of HISs. To address the problem of patient safety, most large hospitals prioritize patients' welfare when building HISs. However, no HIS-associated reduction in adverse events due to medical treatment could be confirmed. HISs are expected to help prevent medical accidents, such as patient- and drug-related errors. It is hoped that the patient safety functions of HISs will become generalized and contribute to patient safety in the future. To achieve this, the government and academic societies should provide regulations and guidelines on HISs and patient safety to the medical community and medical-device vendors. Furthermore, departments responsible for HISs and patient safety should collaborate to gather evidence for the effectiveness of HISs.