The essential oil yields obtained by hydrodistillation of the aerial parts of Hypericum androsaemum cultivated plants varied from 0.94 to 4.09 mg/g of biomass dry weight, depending of the harvest time. The respective analyses performed by gas chromatography and gas chromatography-mass spectrometry revealed more than 80 compounds, 72 of which were identified. Most of the compounds were sesquiterpene hydrocarbons, which, depending of the harvest time, corresponded to 43-78% of the total essential oil. The other compounds were distributed as monoterpene hydrocarbons, oxygen-containing sesquiterpenes, n-alkanes, 1-alkenes, and oxygen-containing monoterpenes, these being a minor group. In H. androsaemum in vitro shoots, sesquiterpene hydrocarbons represented >80% of the respective essential oil. Differences in the essential oil composition were found depending on the harvest time and origin, in vivo versus in vitro, of the plant material. The essential oil sampled in November was characterized by the highest levels of sesquiterpene hydrocarbons and a high number of n-alkanes and 1-alkenes, from C(18) to C(28), whereas that sampled in June of the following year showed the highest levels of n-nonane and 1-octene as well as monoterpene hydrocarbons, the second most representative group.