In this paper results are given of an electron optical investigation of the cross section of optical single films and multilayers obtained by fracture. Direct observation techniques with scanning microscopy and the surface replica technique with transmission microscopy were used. Scanning microscopy is simple in sample preparation but has relatively low resolution. The highest resolution of microstructural details can be obtained only with the replica technique in the transmission microscope. Photographs of ZnS-, MgF(2)-, ThF(4)-, TiO(2), and SiO(2)-films mainly in the form of multilayers and of a cermet-type sun protection film are shown. Some optical film properties, such as refractive index and light scattering, are strongly influenced by film microstructure.