The gas-phase structure of tin(II) acetate, Sn(O ₂ CCH ₃ ) ₂ , has been determined by electron diffraction augmented by flexible restraints derived from ab initio molecular orbital calculations at the DZ(P)/MP2 level. The structure, with C ₂ symmetry, can be regarded as a highly distorted trigonal bipyramid, with the lone pair of electrons on tin occupying one of the equatorial sites. The four-membered rings and the acetate groups were both found to adopt near-planar arrangements. The two equivalent acetate groups are asymmetrically bonded to tin, with Sn–O(4) 233.7(12) and Sn–O(5) 219.2(8) pm, and form a narrow bite angle at tin, with O(4)–Sn–O(5) 58.1(2)°; other important experimental structural parameters (r _a ) are C(2)–O(4) 124.5(5), C(2)–O(5) 127.5(5) and C(2)–C(8) 151.0(5) pm, C(2)–Sn–C(3) 95.1(12), O(4)–C(2)–O(5) 122.0(4) and O(4)–Sn–C(2)–O(5) 176.3(16)° and the acetate groups are twisted about the Sn · · · C axis by 16.8(11)° away from a rhomboidal-based pyramid.