Dear Editor, Hereditary hemorrhagic telangiectasia (HHT, Rendu–Osler–Weber syndrome) is an inherited vascular dysplasia. Typical signs are mucocutaneous telangiectases, epistaxis, gastrointestinal bleeding, anemia, and problems due to large visceral vascular shunts [1]. Little is known about the underlying molecular pathogenetic mechanism; however, unbalanced angiogenesis involving the transforming growth factor-β and vascular endothelial growth factor (VEGF) signaling pathways has been assumed [1]. Phosphoinositide 3-kinase (PI3K) signaling plays an important role in the vascular system via VEGF signaling [2]. Here, we report about a patient with HHT who showed an impressive response during treatment with the pan-class I PI3K inhibitor BKM120.