Dried buckwheat herb is used in medicinal products whereas fresh green plant parts, especially sprouts, are consumed as a vegetable. The herb contains fagopyrins, which cause sensitivity to light after ingestion. The aim of this study was to investigate the impact of different growing conditions and the development phase on the content of fagopyrin and phenolic compounds in buckwheat sprouts. Total flavonoid and total phenol contents, fagopyrin content and antioxidant activity were determined spectrophotometrically. Fagopyrin and flavonoids were located almost exclusively in cotyledons. Based on a comparison to hypericin toxicity, the recommendable intake of buckwheat sprouts was estimated to be less than 40 g per day.