The title solvate, C11H12N4O2S·C4H8O, crystallizes with three molecules of sulfamerazine [4-amino-N-(4-methylpyrimidin-2-yl)benzenesulfonamide] and three molecules of tetrahydrofuran solvent in the asymmetric unit. The dihedral angles between the aromatic rings in the sulfamerazine molecules are 83.40 (12), 87.40 (12) and 89.54 (12)°. In the crystal, molecules are linked by N—H...O and N—H...N hydrogen bonds, generating (10-6) sheets.