The invention relates to a process for preparing polycrystalline silicon, comprising introducing a reaction gas containing hydrogen and silane and/or halogen silane into a reactor, wherein the reactor comprises at least one heated carrier body, on which elementary silicon has been deposited by means of pyrolysis, forming the polycrystalline silicon. In a continuous process, waste gas is led out of the reactor and hydrogen recovered from said waste gas is fed to the reactor again as circulating gas. The circulating gas has a nitrogen content of less than 1000 ppmv. The invention further relates to polycrystalline silicon having a nitrogen component of less than 2 ppba.