Achillea millefolium L. sensu lato (yarrow) is the best-known species of the genus Achillea due to numerous medicinal applications both in folk and conventional medicine. Phenolic compounds such as flavonoids and phenol carbonic acids are present in yarrow and constitute one of the most important groups of pharmacologically active substances. In the present study, yarrow flowers gathered from native populations in different locations of Lithuania were analyzed for phenolic compound composition. High-performance liquid chromatography (HPLC) was used for chemical analyses. Eight phenolic compounds--chlorogenic acid and flavonoids, namely vicenin-2, luteolin-3',7-di-O-glucoside, luteolin-7-O-glucoside, rutin, apigenin-7-O-glucoside, luteolin, and apigenin--were identified in the extracts from yarrow flowers. Considerable variation in accumulation of phenolic compounds among the flowers from different locations was observed. The samples were divided into two main groups based on chemical composition: the first group was characterized by lower than the mean total amount of the identified phenolics; the second was formed from samples accumulating higher concentrations of investigated secondary metabolites. The total amount of the identified phenolics in yarrow flowers from different populations varied from 13.290 to 27.947 mg/g.