The purpose of the research was to assess the price behavior of initial public offerings (IPO) of equities listed on the Warsaw Stock Exchange from 1996 to 2010. We also aimed to observe IPO underpricing and the underperformance phenomenon with different approaches. Short-term performance was analyzed with raw and adjusted initial returns. For the long-term, abnormal returns were compounded and cumulated. Different methods of outliers detection and ways of minimizing the detrimental effect of outliers were applied. In long-term studies, we also compared the results for the daily, weekly and monthly returns. IPO underpricing and underperformance on the WSE still remains substantial and significant, even accounting for the variety of methods applied. The difference in underpricing between the 1996–2004 and the 2005–2010 sample was insignificant. However, we reported statistically significant and economically important differences in underperformance between both samples.