Various factors play a role in the decrease of existence and efficiency of P. brutia forests in the Mediterranean region of Turkey. Insects are one of the most important of these factors. One of the most damaging species is the pine stem borer, Dioryctria sylvestrella (Ratzeburg 1840) (Lepidoptera: Pyralidae). Caterpillars cause great damage to saplings and young trees. In this study, the effect of D. sylvestrella on basal area increment was determined in a Pinus brutia plantations. For this aim, increment cores were obtained from sample trees. In the last four years (2009-2012) all groups (light, moderate, severe and control) were different statistically.