The submillimeter spectrum of ClClO2 has been observed between 365 and 398 GHz in a flowing system as a product of the FClO2 + HCl reaction. Absorptions of three isotopomers, (ClClO2)-Cl-35-Cl-35, (ClClO2)-Cl-37-Cl-35, and (ClClO2)-Cl-35-Cl-37, have been assigned. Rotational and centrifugal distortion constants have been determined and structural parameters derived. The data are compared with those from a matrix-isolation study, ab initio calculations, and related molecules.