The crystal and molecular structure oftrans-dichloro(bis(isopropyl)sulfoxide-S)(1-methylcytosine-N)platinum(II) has been determined by single crystal X-ray diffraction. The crystals are triclinic witha = 16.205(5),b = 8.078(2),c = 6.776(2) Å, α = 106.53(2), β = 96.35(2), γ = 98.54(2)°. The space group isand there are two molecules per unit cell. A total of 2294 independent reflections, of which 2023 were observed, were examined on a Syntexdiffractometer. The structure was refined by full matrix least squares analysis to anR2value of 0.0427. The ligands form a rough square around the platinum atom with Pt—Cl(1), 2.304(3), Pt—Cl(2), 2.287(4), Pt—S, 2.232(2), Pt—N, 2.058(7). Distances within the ligands are normal. The plane of the cytosine ring is at 84.4° to the plane formed by the ligands around platinum.