The title compound [systematic name: 2-cinnamoyl-1,2-benzisothiazol-3(2H)-one 1,1-dioxide], C16H11NO4S, contains both saccharin and cinnamoyl groups. The molecule is approximately planar in the solid state, and adjacent molecules are connected by C-H...O and C-H...pi(phenyl) interactions. In the C-H...pi interaction, the C...CgA distance is 3.916 (4) A (CgA is the non-fused benzene ring centroid) and the C-H...pi angle is 156 (2) degrees . A feature of the molecular geometry is the narrow C-S-N angle of 92.51 (9) degrees in the five-membered ring. This angle relieves strain from the ring and makes it possible for the whole saccharin group to become quite planar.