In the title compound, C7H12N2OS, the 2-sulfanylideneimidazolidin-4-one moiety is nearly planar, with a maximum deviation of 0.054 (2) Å. In the crystal, a pair of N-H⋯O hydrogen bonds and a pair of N-H⋯S hydrogen bonds each form a centrosymmetric ring with an R 2 (2)(8) graph-set motif. The enanti-omeric R and S mol-ecules are alternately linked into a tape along [1-10] via these pairs of hydrogen bonds.