The dielectric properties of CVD diamond films grown by the oxyacetylene flame method for frequency dependent electrical fields have been studied. The dependence of these properties on temperature (from room temperature to 150°C) has also been analysed. The DC conductivity due to free carriers ($\sigma_0$) is obtained for each temperature using the Kramers-Kronig transformations of the experimental data. The values of the conductivity are very low in all cases and close to those of natural diamond ($10^{-16}$ ($\Omega$ cm)$^{-1}$); this is an indication of the low graphite content of the samples. We have also calculated the dielectric losses in the whole frequency range (100 mHz–1 MHz). A study of the relationship between the different deposition conditions with respect to the dielectric properties has been carried out. The microstructure of the films has been characterised with SEM and Raman spectroscopy.