SummaryThe aim of this paper is to analyze the stock market investors reactions to the events of announcement and execution of stock-splits and reverse stock-splits carried out on Warsaw Stock Exchange (WSE) during the period 2004-2012. The study puts the emphasis on the differences between market reactions to standard stock-splits and reverse stock-splits. The results presented in this paper are based on the methodology of event study. The studied data sample consists of 45 instances of stock-splits and 6 instances of reverse stock-splits that took place on WSE in the specified period of time. Results obtained suggest no statistically significant reaction to the events of: split announcement, split execution and reverse split execution and a statistically significant (mostly negative) reaction to the event of reverse split announcement. Although some anomalies can be observed on close inspection of the data, in general the obtained results can be interpreted as evidence of investors' rationality with regards to events connected with stock-splits on the WSE.