The present invention relates to a method of determining the growth of trees based on first and second measurement data obtained at different moments of time by utilizing a laser scanner located above the measured trees. In order to determine the growth of a large number of trees as fast and as easy as possible, said method comprises: processing said first measurement data in order to determine the location of tree locations (A), processing said second measurement data in order to determine the location of tree locations (B), determining the locations which are tree locations according to the results of both said first and second processing (C), and calculating the growth of trees at said determined locations by determining the difference in the size indicated by the second measurement data as compared to the size indicated by said first measurement data (D).