The excitation energy in the multiphoton ionization spectrum of the trans-1-naphthol/N-2 cluster shows only a small red shift with respect to isolated naphthol, indicating a van der Waals pi-bound structure rather than a hydrogen-bonded one. To confirm this interpretation, high-level electronic structure calculations were performed for several pi and hydrogen-bonded isomers of this cluster. The calculations were carried out at the second order Moller-Plesset (MP2) level of perturbation theory with the family of correlation consistent basis sets up to quintuple-xi quality including corrections for the basis set superposition error and extrapolation to the MP2 complete basis set (CBS) limit. We report the optimal geometries, vibrational frequencies, and binding energies (D-e), also corrected for harmonic zero-point energies (D-0), for three energetically low-lying isomers. In all calculations the lowest energy structure was found to be an isomer with the N-2 molecule bound to the pi-system of the naphthol ring carrying the OH group. In the CBS limit its dissociation energy was computed to be D-0 = 2.67 kcal/mol (934 cm(-1)) as compared to D-0 = 1.28 kcal/mol (448 cm(-1)) for the H-bound structure. The electronic structure calculations therefore confirm the assignment of the experimental electronic spectrum corresponding to a van der Waals pi-bound structure. The energetic stabilization of the pi-bound isomer with respect to the hydrogen-bonded one is rather unexpected when compared with previous findings in related systems, in particular phenol/N-2.