Berries of genus <i>Vaccinium</i> are rich in flavonoids and proanthocyanidins (PAs). We studied the PA composition and biosynthesis in bilberry (<i>Vaccinium myrtillus L.</i>) tissues and during fruit development. Soluble PAs, analyzed by UHPLC–MS/MS, were most abundant in stem and rhizome with the mean PA polymerization level varying between 4 and 6 in all tissues. Both A- and B-type PAs were ...