OBJECTIVES: Due to the lack of a short stay unit in the emergency room (ER), patients who need a couple hours of intravenous fluids (i.e. Lasix, insulin, morphine, etc) and observation may be admitted to the hospital. These avoidable hospital days reflect a failure of our healthcare system which contributes to increase health care cost as well as to decrease the number of hospital beds available to other patients. To estimate the magnitude of the problem, this study is purposed to describe the burden of avoidable hospital days. METHODS: Among those admitted to the hospital via ER/urgency care, patients discharged home on the same day they were admitted are considered as an “avoidable hospital day”. Largely, these patients could have been managed with a short observation stay in the ER. The national hospital discharge survey (NHDS-2004) was analyzed to estimate the number of avoidable days. RESULTS: Based on the sampling weight and probabilistic sampling design, the total number of same day discharges was calculated to be nearly 736,000 (95% confidence interval [CI], 703,000- 768,000) in the U.S. during 2004. Among those, 505,000 were admitted via emergency/urgency care; of whom, nearly 322,000 were discharged to home not against medical advice. CONCLUSION: Substantial numbers of hospitalized patients were discharged to home on the same day not against medical advice. Most of them could have been kept out from hospitalization if they were intercalated between the ER and the floor bed. Establishing a short-stay unit in the ER would save substantial financial costs as well as hospital beds for other patients.