There are controversies regarding existing estimates of the size of shadow economy in Poland. Therefore this paper focuses on the measurement of shadow economy in Poland over the period 1995-2007. On the basis of monetary methods, an econometric model for currency demand is built. Using estimation results, the size of shadow economy is assessed. According to the estimates shadow economy declined in the period 1995-2007 starting from 40% of GDP in 1995 and reaching about 10% of GDP in 2007. The paper also analyses relations between shadow economy, state budget and tax system. A Vector Autoregressive model is estimated and Impulse Reaction Functions are drown, showing that an increase in indirect tax burden enlarges shadow economy. A contrary effect arises due to an increase in: a) direct tax burden; b) budget balance.