The essential oils from 14 Achillea cartilaginea samples (leaves and flowers) collected from natural habitats in Lithuania were analysed by GC-MS. In total, 97 compounds were identified, 69 of which have not been reported previously in this species. In general, the essential oils of A. cartilaginea were rich in oxygenated monoterpenes. Remarkable chemical polymorphism was observed within the population of A. cartilaginea in Lithuania. It was observed that 1,8-cineole, camphor, cis-chrysanthenol, β-thujone, sabinol, chrysanthenone, terpinen-4-ol, bornyl acetate and β-sesquiphellandrene were the major constituents in the oils of the analysed plants. Hierarchical cluster analysis, which was based on the 19 major components exceeding 5% in the total oil, indicates the presence of several main chemical groups in the analysed plant populations.