An empirical approach to the description of diffusion paths in the ternary system Fe-Co-Ni is developed. It is shown that the experimentally determined diffusion path in this system can be described by the universal function, which contains two parameters, extracted from experimental data. The values of these parameters and their possible dependence on initial compositions of diffusion couples are discussed. Using the universal function, typical diffusion paths for the system Fe-Co-Ni have been calculated. It is shown that the calculated diffusion paths are in a qualitatively good agreement with the available experimental data.