The mechanisms of atomic diffusion in the cation sublattice of CdTe have been studied. For the present study two types of CdTe layers have been grown by molecular beam epitaxy (MBE) at different Cd/Te flux ratio resulting in different stoichiometry of the matrix material. Each of the samples contained three build-in delta-like markers of MnTe, MgTe and ZnTe. From the spread of the cations out of the markers, caused by a thermal annealing, the diffusivities of Mn, Mg, and Zn were determined by means of secondary ion beam spectrometry (SIMS). We found that the stoichiometry of the CdTe matrix strongly influences on the diffusion activation energy but for a given matrix the activation energy does not depend on the diffusing species. For CdTe layer rich in Cd, the activation energies of cation diffusion for the three investigated cations are found to be around 1.3 eV, while in Te-rich matrix around 1.9 eV. This difference indicates that different diffusion mechanisms operate in these two cases. Assuming the interstitial mechanism in the former case and the vacancy mechanism in the latter, energies of the cation migration in CdTe and of Cd vacancy formation are estimated to be equal to 1.3 and 0.6 eV, respectively.