The room temperature vapor phase CH stretching overtone spectra of trimethylene oxide and trimethylene sulfide are recorded in the Delta upsilon(CH) = 2-7 regions. The spectra are interpreted with the local mode model and are assigned in part on the basis of ab initio calculated CH bond lengths. Ab initio geometry optimizations are carried out at the MP2 level with three different basis sets [6-31G(d), 6-311+G(d,p), and 6-311++G(2d,2p)] for both molecules and with a QCISD/6-31G(d) calculation for trimethylene oxide. Spectral structure not due to pure local mode transitions of to local mode combinations is tentatively assigned to transitions to states that involve the interaction of CH stretching and ring puckering motion.