The chemical composition of the leaf oils are reported for Cupressus arizonica, C. benthamii and C. lindleyi from Mexico and compared to the leaf oil of C. lusitanica, introduced to Portugal in ca. 1634. The oil of C. arizonica has moderate amounts of butyl methyl ether (8.6%), a-pinene (7.6%), β-phellandrene (5.7%), umbellulone (5.4%), isophyllocladene (5.8%), phyllocladene (4.1%), nezukol (8.5%) and phyllocladanol (14.2%). The oil of C. benthamii has a large amount of abietadiene (26%) and trans-totarol (19.3%), with moderate amounts of α-pinene (4.1%), cis-totarol (4.2%) and trans- ferruginol (5 0%). The oil of C. lindleyi has moderate amounts of butyl methyl ether (6.5%), limonene (14.0%), β-phellandrene (13.0%), umbellulone (8.1%), terpinen-4-ol (4.6%) and α-cadinol (10.0%). The oil of C. lusitanica has considerable abietadiene (11–24%), with moderate amounts of α-pinene (6.0–16.6%), sabinene (6.7–10.3%) and trans-totarol (5.1–6.5%). C. lusitanica was about as similar to C. arizonica as it was to C. benthamii or C lindleyi in either terpenoids or Random Amplified Polymorphic DNAs (RAPDs). C. benthamii and C. lindleyi were quite distinct and continued specific recognition seems warranted. C. lusitanica appears to be a distinct taxon but it's origin is still not resolved.