Studies on genetic variability existing in natural populations of Corsican pine are of major concern in developing an optimum tree breeding program. A total of 97 wind-pollinated families grouped into 5 natural stands from the northern part of the Corsican island (Fig. 1, Table I), were raised in a progeny test in Orleans forest and assessed for growth characteristics from age 2 till age 11 after plantation. Measurements of forking defects were also made for the years 1983, 1984 and 1985. Two models for analysis of variance were used: the first one to compare stand means, the second one to compute for each stand estimates of genetic parameters (between-family variances, individual heritabilities, genetic correlations). Phenotypical differences among population means, indicated by discriminant functions, were mainly explained by juvenile growth performances (Table II, Fig. 2, Table III). For these traits, a pattern of clinal variation might exist, depending on an elevational gradient. Genetic parameters varied widely from one stand to another (Table IV, Table V). For growth characteristics, a negative relationship appeared between performance mean and between-family variance value. However, because of a lack of precision in variance components estimation, the hypothesis of homogeneity based on between-family variances, checked by Kullback test could not be rejected for a single given trait (Table VI). Kullback test values computed with special groups of traits showed large discrepancies of genetic structure among the 5 natural stands (Table VII, Fig. 3). Results were discussed referring to two main causes of genetic differentiation of isolated populations: - natural selection pressures, essentially rainfall conditions for Corsican pine in its native range; - genetic drift and factors liable to reduce mean consanguinity rate as could probably be, fire, colonisation of neighbouring areas and human activity.