The vibrational modes in Hg1−xCdxTe epitaxial films and HgTe/CdTe superlattices have been investigated by means of far-infrared (FIR) transmittance spectra at temperatures from 4.2 to 300 K. The observations were put forward in the spectral range from 20 to 350 cm−1, emphasizing the wave-number region at the low-frequency side of the reststrahlen absorption band. A series of single-phonon and two-phonon modes as well as impurities- and defects-induced vibrational modes are observed. FIR transmission seems to be a good probe for characterization of the perfection of Hg1−xCdxTe films.