In this article we aimed at the presentation of important epidemiological issues associated with African Swine Fever. Wild boars are now the main source of African Swine Fever Virus (ASFV), in Poland. In previous years, wild boars have been recognized as the ASF reservoir in Lithuania, Latvia, Estonia and quite recently, in late June of this year, also in Czech Republic. During first half of 2017, 210 cases of ASF were identified in wild boar population in Poland, whereas in 2014 – 30, in 2015 – 53 and in 2016 – there were 80 cases, respectively. It reflects the fast increasing tendency of spreading ASFV in wild boar populations and growing threat for its facilitated transmission to domestic swine. The third wave of ASF in Poland, that has arisen at 7 June 2017, has confirmed this tendency. The high virulence of ASFV currently circulating in Poland and other EU countries, causes high mortality rate, that was confirmed by epidemiological study lasting 40 months. Behavior of wild boars significantly influences the temporal and spatial dynamics of ASF spread. In addition to changing wild boar behavior, ASF dynamics is dependent on factors such as long-distance virus spread by humans. These all may contribute to faster spread of ASFV and the prolonged duration of ASF in wild boars. It should be stressed that from 2013 to June 2017, a natural change in the course of ASF in wild boars has been observed, which is manifested by the increase of number of animals seropositive for ASFV, also called seroreagents or survivors. This also means, that in comparison to years 2014 and 2015, the percentage of wild boars carrying ASFV has grown rapidly, which in turn makes the combat against ASF increasingly complicated.