Previous studies of the microwave rotational spectra ofgaucheCH2DCH2OH have been extended for the torsional ground state and new studies are reported for the first excited states of the –OH torsion. The extended studies for the ground state hydroxylgauche,methyl symmetric conformation made it possible to determine the product of inertia coefficientsDandEas well as the rigid rotorA,B, andCand the centrifugal distortion coefficients ΔJand ΔJK. Likewise for the hydroxylgauche,methyl asymmetric conformations I and II in the ground state rotational coefficients and selected centrifugal distortion coefficients have been determined. Rotational coefficientsBandCand centrifugal distortion coefficients ΔJand ΔJKhave been determined for all of the excited states. A significant result of the spectroscopic search was thatc-dipole transitions were not observed within the range of our spectrometer for either the methyl symmetric or methyl asymmetric conformations in the excited states. For the methyl asymmetric conformation, this means that the tunnelling energy for the excited state has overcome the torsional potential energy term that suppressed the pure hydroxyl tunnelling, that localizes the molecule into conformations I and II for the ground state. The very small tunnelling energy within conformations I and II has been predicted. The role of internal rotation–overall rotation Coriolis coupling including denominator corrections from the rotational energy for hydroxylgauche,methyl symmetric CH2DCH2OH is shown in the Appendix to contribute to the effective rotational coefficients.