This paper addresses the defect structure, as observed by transmission electron microscopy, at a CdTe(111)/GaAs(001) interface. When viewed along the [1(1) over bar0$]CdTe direction, the overlayer exhibits a high density of microtwins parallel to the CdTe(111) growth direction. Meanwhile, when viewed along [11(2) over bar]CdTe, an array of misfit dislocations, exhibiting edge component of Burgers vector equal to a/4[<(1)over bar 10>], a = 6.48 Angstrom, are observed at the interface between the CdTe and GaAs lattices. These misfit dislocations are of such a spacing as to be consistent with only partial relief of the misfit strain. The residual misfit strain is found to relax in a region extending about 200 Angstrom from the interface, with the source of the strain relief being layer dislocations in the CdTe overlayer. The distance over which the misfit relaxes is consistent with the results of X-ray measurements of the misfit relaxation in thin overlayers. Furthermore, the distance over which the misfit relaxes is the same as that which the high density of microtwins are observed, suggesting that the microtwins act as nucleation sites for the observed layer dislocations.