The 2001 Russian tax reform reduced average tax rates for the personal income tax and the payroll or social tax. It also made the tax structure more regressive. Because individuals in the lower income bracket were for the most part not affected, it is possible to estimate the effects of the reform using a differences-in-differences approach. I study the effect of the reform on informal employment. Informality is defined using information on employment registration and self-employment. Applying parametric and semi-parametric techniques, I find evidence that the tax reform led to a significant reduction in the fraction of informal employees. Among the different forms of informality I study, the reform seems to have had the strongest effect on the prevalence of informal irregular activities. I also document stronger effects on individuals who benefited from the largest reductions in tax rates. The strong response to the tax reform lends support to the hypothesis that informal and formal labor markets are well integrated.