['State-supported trauma systems have a proven association with improved mortality, but to date, there are no data reported on what mechanism leads to this benefit. Our hypothesis is that trauma systems with funding support are associated with increased number of trauma centers (TCs).', 'A retrospective population study: data for the number of American College of Surgeons-verified adult TCs in 2010 were obtained from the American College of Surgeons and for state-designated TCs from state departments of health. Population and gross domestic product (GDP) were obtained from the US Census. The main outcome measure was the number of TCs per population and per GDP. Statistical analysis was carried out using the Mann-Whitney U-test and Poisson regression.', 'There was no association between a trauma system and the numbers of level 1 or 2 centers. In states with funded trauma systems, the numbers of level 3 centers per GDP and per million state population were 4.76\xa0±\xa02.37/$100 billion and 1.77\xa0±\xa00.51/million people compared with 0.72\xa0±\xa01.72/$100 billion and 0.28\xa0±\xa00.60/million people for unfunded states (P\xa0<\xa00.05). Poisson multivariate regression identified system funding as an independent predictor of number of level 3 centers.'] Are trauma systems associated with increased level 3 trauma centers?