Correspondence between threading dislocations (TDs) in epitaxial films and the etch pits observed upon selective chemical etching of the samples was studied in Ge/Si(001) heterostructures. It is established that the density of TDs revealed in epitaxial films with thicknesses h ≤ 1 μm can be significantly understated because of insufficient resolution of optical microscopy. Recommendations are given that increase the reliability of PD density estimation by means of structure-sensitive etching.