X-ray characterization of 7-methyl-5,6,7,8-tetrahydro[1]benzothieno [2,3-d]pyrimidin-4[3H]one is described. The compound crystallizes in the monoclinic space group P21/c with a=7.0013(2)Å, b=8.3116(3)Å, c=18.374(6)Å, β=91.746(2)°, V=1068.76(6)Å3, z=4. The structure was solved using the direct method and refined to reliability R-factor of 0.0639 using 3180 independent reflections The crystal structure is further stabilized by intermolecular C-H...N, N-H...N C-H...O, N-H...O, and π-π interactions.