Brejdyny [brɛi̯ˈdɨnɨ] is a village in the administrative district of Gmina Piecki, within Mrągowo County, Warmian-Masurian Voivodeship, in northern Poland. It lies approximately 6 kilometres (4 mi) north of Piecki, 8 km (5 mi) south of Mrągowo, and 55 km (34 mi) east of the regional capital Olsztyn.