Purpose: This study was conducted to compare three discharge criteria; 1) discharge criteria of S Hospital determined by nurses, 2) discharge readiness determined by patients, and 3) the Modified Post-Anesthetic Discharge Scoring System (MPADSS). The usefulness of MPADSS as a discharge criteria for the patients`safe return to home after ambulatory surgery was also evaluated. Methods: A total of 370 day surgery cases were investigated. The MPADSS was employed in every 30 min. in parallel with discharge readiness assessment by nurses and patients. The percentage of the patients who were categorized as being ready to discharge were compared according to three discharge criteria. Results: The percentage of patients scored to be as MPADSS > 9 in 30 min, 60 min, 90 min were 96.5%, 99.5%, 100% respectively. Whereas 11.1%, 44.3%, 71.1% of patients rated themselves as being ready to discharge and 2.7%, 23.5%, 54.3% of patients actually discharged by nurses according to discharge criteria of S Hospital. Conclusion: Nurses tend to keep patients longer in the hospital when compared to the patient`s own assessment about their readiness to home and to that of MPADSS. Faster discharge in the evening than day time suggests patient discharge can be influenced by nursing factors. This brings out the importance of scoring system to determine the safe discharge. The MPADSS could be a useful tool in evaluating patients for safe discharge.