In the title compound, C6H10N2OS, the 2-sulfanylideneimidazolidin-4-one fragment is essentially planar (r.m.s. deviation = 0.0033 Å). In the crystal, one amino group is involved in N-H⋯O hydrogen bonding, which links pairs of mol-ecules into inversion dimers, while the other amino group generates weak N-H⋯S hydrogen bonds, which link these dimers into chains in [10-1]. The chains are further aggregated into layers parallel to the ac plane through weak C-H⋯O inter-actions.