Four histopathological indices of malignancy--cellularity, pleomorphism, vascularity, and necrosis--were correlated with the positive-contrast CT scan in 84 patients with pathologically proved astrocytoma. Vascularity and necrosis correlated best with the scan in supratentorial tumors, while vascularity and cellularity correlated significantly with the scan in cerebellar astrocytomas. These findings indicate that the degree of malignancy of a supratentorial astrocytoma can be inferred from the contrast-enhanced scan, but that this is not generally possible with posterior fossa tumors.