The three mol-ecules in the asymmetric unit of the title compound, C(3)H(4)N(2)O(2)S, are connected via N-H⋯O hydrogen bonds, forming layers normal to [001]. The rings of the mol-ecules are approximately planar, with r.m.s. deviations of 0.0051 (1), 0.0044 (1) and 0.0111 (1) Å.