We implement a quantum Monte Carlo calculation for a repulsive Hubbard model with nearest- and next-nearest-neighbor hopping interactions on clusters up to 12×12. A parameter region where the Fermi level lies close to the van Hove singularity at the saddle points in the bulk band structure is investigated. A pairing tendency in the dx2-y2 symmetry channel, but no other channel, is found. Estimates of the effective pairing interaction show that it is close to the value required for a 40 K superconductor. Finite-size scaling compares with the attractive Hubbard model.