The flavonoid fraction of the aerial parts of Genista cadasonensis Valsecchi (Leguminosae), an endemic plant from Sardinia, was examined and compared with the flavonoid pattern already known in the Genista genus. This comparison evidenced the endemic nature of this species, showing the presence of a rare flavonoid, the 6-hydroxy-genistein. The antioxidant activity of dichloromethanic, ethanolic and acetonic total extracts of aerial parts was evaluated.