A new kind of hydrogen bonding is proposed. It is a pi-electron delocalization-assisted intramolecular dihydrogen bond. This bond is similar to the resonance-assisted hydrogen bonding investigated extensively by Gilli and co-workers (J. Am. Chem. Sec. 111 (1989) 1023). HF and MP2 calculations with 6-311 + + G(d,p), 6-311 + + G(2d,2p) and 6-311 + + G(3d,3p) basis sets have been performed in this study on boron molecules for which intramolecular dihydrogen bonds exist. The atoms-in-molecules theory of Bader is also applied to study these systems.