The roots of the nonpoisonous chemotype of giant fennel (Ferula communis) from Sardinia afforded a novel cadinanetriol (1), whose structure was established by spectroscopic data and confirmed by synthesis from the E,E-Delta (1(10),5) germacradiene allohedycariol. A number of known compounds were also identified. Despite the lack of morphological differences, a broad chemical diversity exists within giant fennel, underlying the contrasting data on its poisonous properties.