The crystal structure of dimethyltin dichloride has been solved and the parameters have been refined by three-dimensional least-squares analysis. The environment of the tin atoms is considerably distorted from the regular tetrahedral co-ordination towards octahedral, because of the association between neighbouring molecules. The Mössbauer spectra of the dialkyltin dichlorides are discussed in terms of this structure, and of the dialkyltin difluorides in terms of a trans-octahedral configuration.