Heterodera achilleae n. sp., a member of the H. rostochiensis group, is described and illustrated from roots of yarrow, Achillea millefolium L. in Sarajevo, Yugoslavia. This new, round-cyst species differs from closely related species especially as follows: (1) from H. leptonepia, by having stouter larvae (a = 21), with longer styler (25 mu), and with outlet of dorsal esophageal gland averaging 5.7 mu from base o f styler; (2) from H. millefolii, in having excretory pore at base of neck and small, straight vulval slit of 5 mu; (3) from H. rostochiensis, in having a B/A ratio (Granek's ratio) of 1.6 ; (4) from H. tabacum, by longer female stylet, two annules on female head, and males with outlet of dorsal esophageal gland further back (5.7 mu). In addition, H. achilleae n. sp. differs from the latter three species in having prominent longitudinal striae on the anterior half, or more, of cysts and females.