We have calculated ab initio the three-dimensional potential energy surface of the LiOH molecule at 166 nuclear geometries spanning energy ranges of about 2500 cm-1 for the LiO stretch, 7500 cm-1 for the OH stretch, and 4000 cm-1 for the bend. The ab initio configuration interaction calculations were performed within the framework of the average coupled pair functional method [R. J. Gdanitz and R. Ahlrichs, Chem. Phys. Lett. 143, 413-420 (1988)]. The equilibrium structure is linear, but we found a very strong interaction between the LiO stretch and the bend such that at longer LiO distances the optimal structure is bent. The rotation and vibration energies for 7Li16OH, 7Li16OD, and 7Li18OH were calculated variationally using the Morse oscillatorigid bender internal dynamics Hamiltonian (MORBID) [P. Jensen, J. Mol. Spectrosc. 128, 478-501 (1988); J. Chem. Soc. Faraday Trans. 2 84, 1315-1340 (1988)]. For 7Li16OH we find that ν1 = 3831 cm-1, ν2 = 289 cm-1, and ν3 = 923 cm-1, and we obtain Be = 1.183 cm-1. The MORBID results are compared with rotation-vibration energies calculated with the nonrigid bender [P. Jensen and P. R. Bunker, J. Mol. Spectrosc. 118, 18-49 (1986)] and semirigid bender [P. R. Bunker and B. M. Landsberg, J. Mol. Spectrosc. 67, 374-385 (1977)] Hamiltonians.