The microwave spectrum of propargyl selenocyanate (HC[triple bond]CCH(2)SeC[triple bond]N) has been investigated in the 40-80 GHz spectral region at 0 degrees C. The spectra of the ground vibrational state of the (80)Se and (78)Se isotopologues of one conformer were assigned. The first vibrationally excited state of the torsion about the CC-Se bond was also assigned for the (80)Se isotopologue. The identified rotamer has a C-C-Se-C antiperiplanar conformation (C(s) symmetry). The microwave work has been augmented by ab initio calculations at the MP2/6-311++(3df,3pd) level and density functional theory calculations at the B3LYP/6-311G++(3df,3pd) level of theory. Both the ab initio and the B3LYP calculations predict that the identified rotamer is the global minimum and indicate the existence of an additional high-energy anticlinal form. The two theoretical methods predict rather different values for the H(2)C-Se bond length as well as for the C-C-Se-C dihedral angle of the high-energy anticlinal form.