Abstract Chromosome numbers for 16 Hieracium s.str. species from Bosnia and Herzegovina, Bulgaria, Macedonia, Montenegro, Poland, Romania and Serbia are given and their metaphase plates are illustrated. Chromosome numbers are published for the first time for H. filarszkyi Jáv. & Zahn 2n = 3x = 27, H. fritschianum Hayek & Zahn 2n = 3x = 27, H. fritzeiforme Zahn 2n = 3x = 27, H. hercegovinicum (Freyn & Vandas) Szeląg 2n=3x=27, H. nivimontis (Oborny & Zahn) Chrtek fil. 2n = 4x = 36, H. vagneri Pax 2n = 4x = 36, as well as three undescribed species of hybrid origin between H. olympicum Boiss. and H. sparsum Friv. 2n = 4x = 36, H. naegelianum Panc. and H. scardicum Bornm. & Zahn 2n = 3x = 27, and H. transylvanicum Heuff. and H. umbellatum L. 2n = 4x = 36.