One of the most important characteristics in determining the dendrometrical properties of a stand is the annual height increment of the trees. On the basis of these increments, natural phases of the trees’ life are defined. In the present study the data concern the height increments of the main trunk of 25-year-old Scots pine, as well as simulated data. Our research deals with the application of longitudinal data analysis. This analysis is usually used when measurements are taken at the same treatments at different time points. The calculations performed provide answers to the question of which annual height increments differ.