The title molecule, C2H6OSe, has a trigonal-pyramidal structure analogous to that of its sulfur analog, dimethyl sulfoxide (DMSO). The Se-O distance in dimethyl selenoxide (DMSeO) is 1.6756 (16) A [versus S-O of 1.531 (5) A in DMSO], consistent with a highly polar bond. In the solid state, the molecules of DMSeO are linked into centrosymmetric dimers formed by two C-H...O hydrogen bonds. These dimers further aggregate into a ladder-like supramolecular network via two additional intermolecular C-H...O interactions. As a result, each O atom of DMSeO acts as an acceptor of three hydrogen bonds.