This study investigates whether flipping activities impose an externality on the transaction prices of the neighboring nonflipped properties. Using a data set of residential property transactions in Clark County, Nevada for the period 2003-2013, we find that flippers impose a significant positive impact on the price of neighboring nonflipped properties in an up market, but a significant negative effect in a down market. This procyclical impact of flipping activity contributes to the volatility of housing prices, hence magnifying boom and bust cycles and increasing the likelihood of a mortgage crisis.