On the basis of the results of the experimental IR studies of matrix reactions between methylsilanes and oxygen atoms, Withnall and Andrews have postulated the possibility of the existence of equilibrium between two farms of Me(OH)Si=CH2. in order to verify their supposition, an ab initio study at various levels of theory was performed. Two hydroxy forms of methylsilaethylene were fully optimized using the gradient procedures at the MP2 and DFT(Becke3LYP) approximations with the standard 6-311G(d,p), 6-311G(2d,2p), and 6-311G(2df,2pd) basis sets. Harmonic vibrational frequencies were calculated at all levels. The MP4-(SDQ)/6-311G(2df,2dp)parallel to MP2/6-311G(2df,2p) + ZPE(MP2) calculations establish the energy difference between cis and trans isomers at 1.9 kcal/mol, which makes both forms experimentally accessible. Vibrational frequencies and shifts of frequencies upon isotopic O-18 and deuterium substitutions predicted at the MP2 and DFT levels correlate well with the experimental data, thus supporting assignments of vibrational bands and identifications of reaction products by Withnall and Andrews.