An nb initio potential energy surface for the quartet electronic state of NH3+ has been constructed at the MP2/6-31G(d,p) level of theory. The accuracy of this surface has been verified by comparison with high levels of theory. Classical simulations of the collision of N(S-4) and H-3(+)((1)A(1)＇) showed no reaction to form NH2+ + H at thermal energies. The possibility of reaction via surface hopping to the doublet electronic state has been investigated by calculation of the quartet-doublet energy gap at the MRCI/6-311+G(2df,p) level of theory. No evidence of surface crossing could be found for configurations accessible at thermal energies.