The first stable chlorosilylene-BH3 adduct was synthesized in the reaction of N-heterocyclic carbene (NHC) stabilized dichlorosilylene either with equivalent amounts of LiBH4 or with equivalent amounts of a BH3 center dot THF solution. The chlorosilylene-BH3 adduct was characterized by single-crystal X-ray structural analysis, NMR and IR spectroscopy, EI mass spectrometry, and elemental analysis.