The crystal structure of the title compound has been determined by single-crystal X-ray diffraction. Crystals are monoclinic, space group P21/n, with Z= 4 in each unit cell of dimensions a= 9·5208(24), b= 13·1583(36), c= 16·5437(40)Å, β= 93·600(17)°. The structure was solved by the heavy-atom method and refined by full-matrix least-squares methods to R 0·049 for 1896 independent reflections. The tin atoms are octahedrally co-ordinated by a bidentate 2,2′-bipyridyl residue, two cis-chlorine atoms, and two phenyl groups which are mutually trans. The two tin–carbon bond distances are identical [mean r(Sn–C) 2·152 Å], as are the two tin–chlorine bond distances [mean r(Sn–Cl) 2·509 Å]. The bipyridyl group is not planar, one C5H4N ring being twisted 4·2° with respect to the other, with the two Sn–N distances unequal (2·344 and 2·375 Å). The bond angles subtended at tin by adjacent ligands all fall in the range 85·5–95·6°. The two phenyl groups are not exactly trans(C–Sn–C 173·5°), and are not equivalent. The plane of one phenyl group almost exactly bisects the Cl–Sn–Cl and N–Sn–N bond angles, whilst the other is rotated 79·5° with respect to the first.