In 2018 the Polish government announced a new law on investment incentives which will substitute the present special economic zone (SEZ) regime. The latter has been in operation since 1994 and was intended to correct some market imperfections at regional level. This change may suggest that SEZs have not met the expectations of politicians or that the future investment policy will need different tools. The aim of this paper is to evaluate whether SEZs were attractive for investors and what was their impact on the Polish economy. The effectiveness of SEZ policy will be assessed on the basis of comparative analysis of empirical studies which were conducted by Polish and foreign researchers. Most of such publications are available only in Polish. As a result of the language barrier, SEZ policy achievements and failures in Poland are much less known internationally than their records in China and other developing countries. The empirical studies on Polish SEZs differ together with methods, sources of data and periods covered. Due to the lack of data (e.g. on production, exports or technical progress), most studies were devoted to the impact on jobs and investment, i.e., to the static effects. Majority of them were descriptive, not based on any theoretical framework. Their results show that, generally speaking, SEZ effects were positive. However, researchers who verified them formally, either with statistical or econometric methods, did not provide conclusive results. To a large extent methods used in them determined the answers which were obtained. Further studies are important for a reliable evaluation of investment incentives, especially of their indirect impact on the economy. Also the estimates of costs of incentives are usually neglected by researchers. The results of such studies could help in shaping a more rational investment policy.