In this study, major types of flavonoids in 7-day sprouts of five common buckwheat cultivars grown in Poland (Hruszowska, Kora, Panda, Luba and Emka) and wild tartary buckwheat were investigated. Results demonstrated that sprouts of common buckwheat cultivars and wild tartary buckwheat contained both known and a newly discovered flavonol: quercetin 3-O-galactosyl-rhamnoside. An exceptionally high content of this flavonoid was found in cotyledons of wild tartary buckwheat (30.79 ± 0.14 mg g−1 DW), exceeding about 10 times level of rutin (3.16 ± 0.07 mg g−1 DW). The results are not consistent with the data published so far on the content of flavonoids in sprouts of tartary buckwheat. Higher levels of flavonoids were measured in cotyledons than in hypocotyls with the exception of anthocyanins, which were present in higher amounts in hypocotyls. Cotyledons of common buckwheat sprouts were rich in C-glycosides of luteolin and apigenin, the total content of which exceeded ca. 5 times the concentration of rutin.