The rotational spectrum of the hydrogen-bonded dimer formed between 3,3-dimethyloxetane and hydrogen chloride has been investigated in the region 6-18 GHz using a molecular-beam Fourier transform microwave spectrometer with a dual-flow injection system. A single axial conformer has been observed for the complex in the supersonic jet. A C-S-symmetry effective structure has been derived from the rotational parameters of the parent, Cl-37- and C-13-monosubstituted species in their natural abundance, with HCl forming an axial hydrogen bond to the oxygen atom of the ring of 3,3-dimethyloxetane. The non-observation of a plausible equatorial conformer is discussed. (C) 2004 Elsevier B.V. All rights reserved.