The energy surface of CaOH has been studied and an isomer of the form of HCaO with an electronic state of (2) Sigma(+) symmetry has been found. It is linear with H-Ca and Ca-O bond lengths of 2.021 and 2.002 Angstrom, respectively, at the CISD level with a basis set of triple-zeta plus double polarization quality. The overall electronic structure is largely ionic and can be described as H(1s(2))Ca(4s(0))O(2s(2)2p(x)(2)2p(y)(2)2p(z)(1)) (H-Ca2+O-). The minimum on the energy surface is well defined and the harmonic vibrational frequencies have been calculated. The O-H bond length and stretching frequency and the bending frequency of CaOH have also been calculated and compared with experiment.