Giant cell nuclear DNA, in 30 giant cell lesions of the jaws, was quantified by computer-assisted image analysis. DNA 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 DNA content was quantified by the Leitz Texture-Analysis-System-Plus. DNA in nuclei of normal appearing stromal fibroblasts (n = 20) was similarly measured. The DNA index was calculated as the mean nuclear DNA content of giant cells divided by the mean DNA 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 DNA content of giant cells is not useful as a predictor of the clinical behavior of giant cell lesions of the jaws.