The microwave spectrum of sulfur dioxide (SO2) is critically reviewed and supplemented with spectral frequency calculations derived from rotational and centrifugal distortion terms in the molecular Hamiltonian. The primary objective of this review is to provide the microwave transition frequencies applicable to molecular radio astronomy for the ground vibrational state of the most abundant isotopic forms, i.e., the singly substituted atoms33S and34S. Also included is an analysis of the lowest lying vibrationally excited state (&ngr;2=1) of32S16O2. The frequency limits and maximum rotational quantum value (J) vary for each isotopic form but for32S16O2the frequency range 100 MHz to 650 GHz is presented forJmax=60.