In this paper, one application of the Waring's method to estimate leaf area index, in Pinus sylvestris, is presented. Cross-sectional sapwood area was measured at different heights in four trees and was related to the leaf area sustained over each stem point. A satisfactory correlation between both variables was found, the coefficient of determination being 0.9 and the relationship between leaf area (m2) and sapwood area (cm2) was 0.18. A way to estimate leaf area index of the forest is presented and a few aspects related with functional and structural problems of Pinus sylvestris are discussed.