The reaction of ground state boron atoms, B-11(P-2(j)), with allene, H2CCCH2(X(1)A(1)), was studied under single collision conditions at a collision energy of 21.5 KJ mol(-1) utilizing the crossed molecular beam technique; the experimental data were combined with electronic structure calculations on the (BC3H4)-B-11 potential energy surface. The chemical dynamics were found to be indirect and initiated by an addition of the boron atom to the pi-electron density of the allene molecule leading ultimately to a cyclic reaction intermediate. The latter underwent ring-opening to yield an acyclic intermediate H2CCBCH2. As derived from the center-of-mass functions, this structure was long-lived with respect to its rotational period and decomposed via an atomic hydrogen loss through a tight exit transition state to form the closed shell, C-2v symmetric H-C C-B=CH2 molecule. A brief comparison of the product isomers formed in the reaction of boron atoms with methylacetylene is also presented.