This study aimed to elaborate and develop the existing methods used in inventorying lowland forest and adapt them for mountainous forests. The inventory of mountain forests with the use of CIR aerial photographs in this study relied on the implementation of the 3D (three-dimensional) methods and it was characterised by two phases. In the 1st p hase the auxiliary variables (e.g. crown cover, height of dominant trees, density) were measured on the aerial photographs (355 circular plots). Variable of interest (standing volume) was recorded during the terrestrial survey on the corresponding ground sample plots. A statistical relationship was established between the variable of interest and the auxiliary variables by means of multiple regressions. In the 2nd phase selected auxiliary variables were measured on the enlarged set of 2772 plots on the aerial photographs only. The variable of interest (standing volume) was computed for the whole forest area by using the regression model developed in the 1st phase and t he aid of the variables measured in the 2nd phase.