The crystal and molecular structure of 1,1-dichloro-2,2-bis[p-(N,N- dimethylamino)phenyl]ethane, a structural analogue of the degradation product of the insecticide DDT, has been determined from three dimensional diffractometric data using Mo-Kα radiation. The compound crystallises in the monoclinic space group P21/c with unit cell dimensions a = 8.091(4), b = 6.145(2), c = 34.384(10) Å, β = 91.50(3)°. The structure was solved by direct methods and refined by full-matrix least-squares analysis to a final R value of 0.075 for 1 522 observed reflections. The ethylenic double bond distance is 1.328(11) Å. The twist about the ethylenic bond is 7.1(5)°. The C-Cl distances are 1.731(9) and 1.743(8) Å. The conformational parameters of this compound are compared with those of other analogous insecticides studied by X-ray diffractometry methods. The conformational angles are low in comparison with the other active insecticides.