OBJECTIVES: Day surgery has been introduced in numerous heath care systems and has been proved able to save resources and promote efficiency and effectiveness. The aim of this study is to estimate the savings that can be realized by the adoption of day surgery by the Greek National Health System. METHODS: Surgery procedures were classified according to the type of anesthesia and the post-operative care they require. The procedures identified as suitable for day surgery, according to the above criteria, were matched to the Greek Diagnostics Related Groups (DRGs). The possible savings were calculated on the basis of the marginal cost these procedures impose to hospitals when treating them as inpatient surgeries. Savings were estimated for both the social insurance(SI) and for the government budget due to the fact that SI reimburses the capital production factor of each DRG while the labor cost is funded by the government budget. RESULTS: 62 DRGs were identified as suitable for day cases. The majority of these were procedures of the eye (16%), the ear, nose and throat (11.3%), the myoskeletal system (9.7%), the kidney and the urinary tract (9.7%) and the female reproductive system (9.7%). The hospital marginal cost of an increase in the length of stay by one day was estimated at 563.32 euros (95%CI: 541.6–585.1). The annual savings were estimated at 93.7 million euros for the SI and when labor opportunity cost is included the amount saved exceeds 225 million. CONCLUSIONS: In light of the economic crisis and the continuously reduced health care budget, the health system should adopt cost-effective intervention in order to preserve a satisfactory level of health services output. As this study concludes, day surgery can save a great amount of resources and according to the international literature can also guarantee patients’ safety and satisfaction.