The study analyzes the accuracy of indirect estimates one of the main foliage characteristics such as total foliage area of isolated trees with the Plant Canopy Analyzer LAI-2000 (LI-COR, Lincoln, NE, USA). The essay considered two forest species characterized by different foliage and crown architecture as wild cherry (Prunus avium L.) and common walnut (Juglans regia L.). Estimates with the LAI-2000 were compared with references values obtained with the harvesting method (total defoliation). Three different sampling procedures, based on different azimuth angles of measurements, were compared. Results showed the significant role played by crown architecture and total foliage area in the accuracy of estimates; conversely, no significant difference was found using the three different sampling procedures. The correlation between the estimates of foliage characteristics with the LAI-2000 and the values obtained with the reference method was linear and with significant correlation coefficients (P<0.01) both for wild cherry and common walnut. Results accounted for a reliable use of LAI-2000 to assess temporal and spatial variations of foliage characteristic of isolated trees. Collection of direct reference measurements is strongly recommended to know exactly foliage characteristics and in order to assess instrument performance for a given species.