In the title compound, C(12)H(13)NO(3)S, a saccharin derivative, the dihedral angle between the aromatic and isothia-zole rings is 2.91 (12)°. The planar 3,3-dimethyl-allyl group [maximum deviation = 0.0086 (16) Å] is oriented at dihedral angles of 71.86 (7) and 74.35 (7)° with respect to the aromatic and isothia-zole rings, respectively. In the crystal structure, weak inter-molecular C-H⋯O inter-actions link the mol-ecules into chains along the c axis. A weak C-H⋯π inter-action is also present.