The Bereza Kartuska detention camp (or concentration camp; Polish: Miejsce Odosobnienia w Berezie Kartuskie, "Place of Isolation at Bereza Kartuska") was a Polish place of detention, principally for political prisoners, that was operated in 1934–39 at Bereza Kartuska in the former Polesie Province (today in Belarus, near the city of Brest).According to incomplete data from Soviet sources, at least 10,000 people had gone through the prison. Prisoners included members of the Organization of Ukrainian Nationalists (OUN), Polish Communist Party (KPP) and National Radical Camp (ONR), as well as members of the Peasant Party (SL) and Polish Socialist Party (PPS). The detainees included Boleslaw Piasecki and, for some dozen days, the journalist Stanislaw Mackiewicz (the latter, paradoxically, a warm supporter of the prison's establishment). Also a number of Belarusians who had resisted Polonization found themselves in the camp.
The first inmates—ONR activists—arrived on July 17, 1934. A few days later, OUN activists arrived: Roman Shukhevych, Dmytro Hrytsai and Volodymyr Yaniv.
All political prisoners, including prominent Ukrainian political activists such as Mykola Lebed and Stepan Bandera, were freed by Polish authorities in early September 1939. The intention was to spare prisoners the trials of German captivity.
Ukrainian historian, Viktor Idzio, states that according to official statistics, 176 men – by unofficial Polish statistics, 324 Ukrainians – were murdered or tortured to death during questioning, or died from disease, while escaping, or disappeared without trace. Most were OUN members.
In early 1938, the Polish government suddenly increased the number of inmates by sending 4,500 Ukrainians to Bereza Kartuska without right of appeal.