We report a combined spectroscopic and theoretical investigation of the intel-molecular vibrations of supersonic jet-cooled phenol .(H2O)(3) and d(1)-phenol .(D2O)(3) in the S-0 and S-1 electronic states. Two-color resonant two-photon ionization combined with time-of-flight mass spectrometry and dispersed fluorescence emission spectroscopy provided mass-selective vibronic spectra of both isotopomers in both electronic states. In the S-0 state, eleven low-frequency intermolecular modes were observed for phenol .(H2O)(3), and seven for the D isotopomer. For the S-1 state, several intermolecular vibrational excitations were observed in addition to those previously reported, Ab initio calculations of the cyclic homodromic isomer of phenol .(H2O)(3) were performed at the Hartree-Fock level, Calculations for the eight possible conformers differing in the position of the "free" O-H bonds with respect to the almost planar H-bonded ring predict that the "up-down-up-down" conformer is differentially most stable. The calculated structure, rotational constants, normal-mode eigenvectors, and harmonic frequencies are reported. Combination of theory and experiment allowed an analysis and interpretation of the experimental S-0 state vibrational frequencies and isotope shifts.