Giant cell nuclear D N A , in 30 giant cell lesions of the jaws, was quantified by computer-assisted image analysis. D N A content was then used to predict clinical behavior and outcome. 4 nuclei in each of 25 giant cells (total = 100 nuclei) were randomly selected and the D N A content was quantified by the Leitz Texture-Analysis-System-Plus ®. D N A in nucleii of normal appearing stromal fibroblasts (n = 20) was similarly measured. The D N A index was calculated as the mean nuclear D N A content of giant cells divided by the mean D N A content of control fibroblasts. The mean DNA-index of aggressive lesions (1.09, SD = 0.12) was not significantly different from that of non-aggressive lesions (1.18, SD = 0.15) (p = 0.093). The results indicate that the nuclear D N A content of giant cells is not useful as a predictor of the clinical behavior o f giant cell l e s ions of the jaws.