Background: Study of the medico economic impact of enhanced rehabilitation after surgery (ERAS), by comparing the cost of patient care with or without ERAS, both from the point of view of the hospitals and the Social Security Health Insurance Program. Methods: Retrospective longitudinal study on matched data from March 1, 2019 to December 31, 2019. The data are extracted from the French prospective payment system. We studied 12 of the most commonly performed in ERAS business segments. The primary outcome was the reduction of the average length of hospital stay and its implications on production costs and excess capacity. We also studied the impact on hospital incomes and Social Security Insurance Program expenses. The potential gain in hospital days was computed by comparing the length of stay of ERAS and non-ERAS cases. The cost reduction was estimated using the mean number of avoidable days of hospitalization, and the mean cost of the stays obtained from the national cost study. Finally, we studied an approximation of the additional expense for the Social Security Health Insurance Program on costs standardized by applying public sector rates. Results: The average length of stay reduction attributed to ERAS is 1.45 (CI 95% 1.42 to 1.48) day per stay, translating to a cost reduction for the hospitals of € 1060 (CI 95% 995 to 1125) per patient and a total of €65 million (CI 95% 61 to 69). At the same time, the additional expenses for the Social Security Insurance Program can conservatively be approximated to € 1.6 million, breaking into a € 2.2 million increase partially compensated by cost savings of € 0.6 million over subsequent stays for complications. Overall, for each percent of additional ERAS activity over the scope of the study, the marginal cost reduction for the hospitals can be estimated to € 1.8 million (CI 95% 1.7 million to 2.0 million). Conclusions: Associated with previously known clinical benefits for the patients, these convincing results in terms of economic gain strongly support expanding the adoption of ERAS.