Chromosome numbers of 17 taxa of Hieracium s.str. from Bulgaria, Greece, Poland and Romania are specified and their metaphase plates are illustrated. Chromosome numbers are published for the first time for H. engleri R. Uechtr. (4x), H. kritschimanum Mattfeld & Zahn (3x), H. latifolium Link (3x), H. tephrosoma subsp. amaurocranum Zahn (5x), as well as five undescribed species belonging to the H. lachenalii agg. (3x), H. rohacsense agg. (4x), H. vagneri agg. (4x), H. vranjanum agg. (4x) and H. wiesbaurianum agg. (3x), and a new hybrid between H. caesium s.lat and H. umbellatum (4x).