Background: Some clinical questions are best answered by a database study design, and the two Danish Hernia Databases have been a driver of both national and international hernia research for many years. We wanted to give a detailed overview of the currently registered data in the Danish Inguinal Hernia Database and the Danish Ventral Hernia Database. Methods: The Danish Inguinal Database was launched in 1997, and the Danish Ventral Hernia Database in 2007. It is mandatory for Danish surgeons to enter operative data after each hernia repair, both in public and private hospitals. The variables in the two databases have been updated regularly. Results: The two databases started with quite simple registration forms and have over the years developed into more complex registries. In the article we give a detailed overview of the currently registered data in the two databases. During the period January 1, 1998 to December 31, 2019 a total of 181,715 patients were registered in the databases. For inguinal hernia repair through the lifespan of the database, 22% were done by laparoscopy and 62% by Lichtenstein repair. There was about twice as high reoperation rate for recurrence for bilateral compared with unilateral hernias. Ventral hernias in the database comprised 54% umbilical hernias, 23% incisional hernias, and 15% linea alba hernias. For ventral hernias we observed decreased use of intraperitoneal mesh placement and increased use of onlay procedure. In recent years the use of laparoscopic technique for ventral hernia repair has slightly decreased and open procedures slightly increased. Conclusions: The two Danish hernia databases register all hernia repairs in Denmark where it is mandatory for surgeons to enter operative data after each operation. Variables have been updated several times over the years when new scientific questions needed answers. National databases give the opportunity to follow development in daily clinical practice and to answer important scientific questions.