The structure of the title S-alkylated isothiosemicarbazide, C(12)H(15)N(3)OS, was determined by single-crystal diffractometry and compared with the structures of other compounds containing the S-alkylthiosemicarbazide moiety. Such structures cluster into two groups, according to the different orientation of the [bond]SR group with respect to the hydrazine N atom of the thiosemicarbazide. The cis arrangement is preferred by most molecules in the solid state, in spite of the possibility of intramolecular N[bond]H...N interactions in the opposite orientation.