Hydro-distilled essential oils of mature seeds of Zanthoxylum alatum DC. from nineteen populations of the North-Western Himalaya (Uttarakhand, India) were analysed using GC and GC/MS techniques to determine the intraspecific chemical variability. Altogether, 39 compounds were identified in the oils, and a relatively high variation in their contents was found. The oils were dominated by monoterpene hydrocarbons (17.44–68.53%) and oxygenated monoterpenes (13.53–69.12%). The main constituents of the essential oils were linalool (3.5–46.5%), limonene (0.82–41.5%), β-phellandrene (0.24–37.6%), terpinen-4-ol (0.02–21.9%), 2-undecanone (0.16–18.2%), sabinene (0.34–17%), E-methyl cinnamate (0.02–15.7%), 1,8-cineole (0.03–15.2%), myrcene (0.65–13.8%) and trans-caryophyllene (0.04–10.66%). For the determination of the chemotypes and the intraspecific chemical variability, the essential oil components were subjected to cluster analysis. The five different chemotypes characterized were Chemotype I (limonene), Chemotype II (linalool/ sabinene/ 2-undecanone), Chemotype III (linalool), Chemotype IV (limonene/ b-phellandrene/ linalool) and Chemotype V (b-phellandrene/ linalool/ sabinene).