Potential energy surface (PES) of thiourea, SC(NH 2 ) 2, has been searched for stable conformers under C 1 , C s , C 2 , and C 2v symmetry constraints by post-Hartree-Fock ab initio methods with electron correlation level varying from second-order Moeller-Plesset perturbation theory (MP2) to quadratic configuration interaction with single and double excitations (QCISD) and basis sets of double-and triple-zeta quality within 6-311G(d,p) to aug-cc-pVTZ range. Thiourea conformers of C 2 and C s symmetry have been found as stationary points on the PES with no imaginary frequencies at MP2/6-311G(d,p) level, whereas only the C 2 conformer seems as true minimum when basis sets containing more polarization and/or diffuse functions were used. At QCISD/cc-pVTZ level, only the C 2 thiourea conformer has been found as true minimum on the PES. Anharmonic vibrational spectra of C 2 conformers of thiourea and thiourea-d 4 have been computed by vibrational self-consistent field (VSCF) and correlation-corrected VSCF methods using quartic force field approximation at MP2/TZV1(2d,2p), and MP2/6-3111G(3df,2p) level and direct approach at MP2/6-311G(2d,p) level. Both quartic force field and direct VSCF methods used PES expansion in curvilinear (internal) coordinates. Wavenumbers of fundamental, first overtone, and combination transitions of C 2 symmetry conformer have been calculated for natural abundance thiourea and thiourea-d 4 isotopomer. Anharmonic corrections originating from mean field and mode coupling effects vary from 5 to 60 cm 21 , whereas mode-mode correlation contribution seems significant in the case of m(N-H) stretching and d(NH 2 ) deformation modes (15-5 cm 21 ). Application of internal coordinates in the VSCF calculation results in slight underestimation of d(NH 2 ) deformation mode fundamentals and correct description of out-of-plane large-amplitude s(SCNH) modes.