Maintaining a balance between work and disease treatment or prevention has become a major social issue in Japan because of the aging labor force and low birth rate. The harmonization outlined here aims at meeting two important challenges with regard to preventive medicine: protection against workers’ illness exacerbation (PWE) and supporting fitness for returning-to-work (RTW) patients. There is much room for improving PWE, especially for lifestyle-related diseases, such as diabetes mellitus, hypertension, and some cancers. More than 80% of the high-risk examinees of non-communicable diseases do not visit medical institutions during the 1-year period after a health check-up, although approximately half of individuals with an extremely high risk of diabetes visit physicians at least once. Several problems are related to RTW, such as repeated sick leave by employees for mental disorders and the short sick leaves available for cancer-diagnosed patients.
 In 2016, the Japanese Government and the Ministry of Health, Labour, and Welfare of Japan published guidelines for balancing work and disease treatment in the workplace. According to these guidelines, collaboration between medical institutions and workplaces through employee-approved medical information exchange is important. This collaboration means cooperative support for the empowerment of workers with diseases controlled by general clinical medicine and occupational medicine. An effective social system that acts as a sturdy bridge between clinics and companies (C&C) should be developed to promote harmonization of work with illness treatment or prevention in the context of PWE and RTW.