This paper provides empirical evidence on the long run effects of tax policy on income concentration in Switzerland. As Swiss cantons enjoy considerable autonomy with respect to income taxation, it is possible to study the impact of the cantonal income tax burden, as well as the influence of tax competition, on cantonal top income shares. Using panel regressions covering all Swiss cantons from 1917 to 2009 we find the expected negative effect of the tax burden on the cantonal top income share. Further, we find evidence that tax competition is a driving force behind the income shares of the top 1, 0.5 and 0.1 percent. Lower tax rates in neighbor cantons induce competitive pressure and ceteris paribus reduce top income shares in a canton. For the very top incomes tax competition seems to be an issue of the last 30 years.