The purpose of this research was to test the precision of a diameter increment model for the estimation of future periodic diameter increment. Individual trees of Crimean pine (Pinus nigra Arnold) and Calabrian pine (Pinus brutia Ten.) located in both natural and plantation stands were selected. For that reason, normal closed canopy, pure, even-aged and undisturbed stands were examined. In 2002, plots were sampled in three natural and three plantation stands in Isparta region of Turkey. The number of sampling points in sample plots ranged from 19 to 55. In each sampling point, a subject tree and six competitors were selected. In each sampling point, subject tree and competitor trees were stem mapped (x and y coordinate system), and diameter (dbh), total height, age, and 10-yrs radial increment recorded. The predictors of a distance dependent diameter increment model were chosen that included tree level (diameter (d), competition index (CI), and age (t)) and stand level (basal area (G), and site index (SI)) characteristics as well as their transformations. The best fit index of the regression model was pursued in trials with variable combinations. The models explained 65%, 60%, 68% and 50% of the variation in individual tree diameter increment of Crimean pine and Calabrian pine for both natural and plantations stands, respectively. These models can be estimated diameter increment of individual trees at highly significant level (p < 0.001).