The sample of the title compound, C12H15N3S, chosen for study consisted of triclinic crystals twinned by a 180° rotation about the a axis. The five-membered ring adopts a twisted conformation. The dihedral angle between the phenyl ring and the mean plane of the thio-urea unit is 78.22 (8)°. In the crystal, molecules are linked via pairs of N-H⋯S hydrogen bonds forming inversion dimers.
