context: in the past few years, an increasing interest in the volatile secondary metabolites of hypericum perforatum l. (guttiferae) has been arising. objective: the present study is a contribution to better understand the relationship between the morphological variations and volatile composition during the phenological cycle. materials and methods: leaves at the stages of vegetative, floral budding, flowering and green capsule, buds, full opened flowers and green capsules were assayed for essential oil (eo) components by gas chromatography-flame ionization detector (gc-fid) and gc-mass spectrometry (ms). results: significant amounts of sesquiterpenes (oxygenated 26-50% and hydrocarbons 20-40%) and oxygenated hydrocarbons (13-38%) characterized the all analyzed samples showing peculiar fluctuations during the seven phenological stages. although monoterpenes were present in much lower amounts (monoterpene hydrocarbons 0.4-6%; oxygenated monoterpenes 0.8-6%) they were considered also important discrimination for several stages. the green capsules and the full opened flowers collected at flowering stage were clearly distinguished in terms of eo compositions from the other samples. discussion: for the first time, the eo composition of turkish wild hypericum perforatum was monitored by the hydrodistillation of different plant organs collected at different seven stages in order to point out the modification of target volatiles related to each phenological step. conclusions: based on the eo composition monitored during these seven morphological stages by gc-ms, principal component analysis and cluster analysis, significant metabolite modifications were observed during the phenological cycle which involved the levels of specific volatile target compounds belonging to the chemical classes of hydrocarbons, monoterpenes and sesquiterpenes.