The additional health-promoting properties of functional virgin olive oil (FVOO) enriched with its own phenolic compounds (OOPC) versus the parental virgin olive oil (VOO) must be tested in appropriate human clinical trials. Our aim was to assess the effects of FVOO on endothelial function in hypertensive patients. Thirteen pre- and stage-1 hypertensive patients received a single dose of 30 mL of FVOO (OOPC = 961 mg/kg) or VOO (OOPC = 289 mg/kg) in a postprandial randomised, double blind, crossover trial. Endothelial function, measured as ischemic reactive hyperemia (IRH) and related biomarkers, were followed for 5 h after consumption. Compared with VOO, FVOO increased IRH (P < 0.05) and plasma Cmax of hydroxytyrosol sulphate, a metabolite of OOPC 2 h postprandial (P = 0.05). After FVOO ingestion, oxidised LDL decreased (P = 0.010) in an inverse relationship with IRH AUC values (P = 0.01). FVOO provided more benefits on endothelial function than a standard natural virgin olive oil in pre- and hypertensive patients. Trial registration: isrctn.org. Identifier ISRCTN03450153