Objectives: The objective was to estimate emergency physician (EP) workforce needs, taking into account the diversity of U.S. emergency departments (EDs) and various projections of EP supply and demand.Methods: The 2005 National ED Inventory-USA (http://www.emnet-usa.org/) provided annual visit volumes for 4,828 U.S. EDs. The authors calculated annual supply based on existing emergency medicine (EM) board-certified EPs, adding newly board-certified EPs, and subtracting board-certified EPs who died or retired. Demand was estimated at each ED by dividing the number of visits by the average EP volume (based on 2.8 patients ⁄ hour, 40 hours ⁄ week, and 34% nonclinical time). The models assumed that at least 1 EP should be present 24 ⁄ 7 in each ED, which would require at least 5.35 full-time equivalents (FTEs) per ED. Based on annual EP attrition estimates, results for best-case, worst-case, and intermediate scenarios were calculated.Results: In 2005, there were approximately 22,000 EM board-certified EPs, but 40,030 EPs would be needed to staff all 4,828 EDs (55% of demand met). A total of 2,492 (52%) EDs had a visit volume that required the minimum number (5.35) FTEs, of which 47% were rural. In the unrealistic (no attrition), best-case scenario, it would take until 2019 to staff all EDs with board-certified EPs. In the worst-case scenario (12% attrition), supply would never meet demand. Our intermediate scenario (2.5% attrition) suggested that board-certified EPs would satisfy workforce needs in 2038. The report states that ''although, ideally, all EDs [emergency departments] would be staffed by residency trained, board certified EPs, this is highly unlikely to occur in the near to middle term, if ever. Therefore alternative staffing models must be developed.'' Staffing EDs creates unique challenges due to the mandate to provide round-the-clock care and the inability to restrict patient demand for services. The most recent national EP workforce projection, based on 1999 data, 2 questioned the ability to supply an adequate number of emergency medicine (EM) residency-trained, board-certified EPs. Given the rising volume of ED visits, up to 115 million in 2005,3 and changes in the political landscape, 4 a reassessment of EP workforce needs is warranted.Our objective was to estimate EP workforce needs, taking into account the diversity of U.S. EDs and various projections of EP supply and demand. We hypothesized that the supply of EM residency-trained, board-certified EPs would be insufficient to meet demand for several decades.