The tall cell variant of papillary carcinoma of the thyroid manifests a more aggressive behavior than the usual form of papillary carcinoma of the thyroid. Morphometric analysis of nuclear features and DNA analysis may yield information predictive of aggressive behavior. Accordingly, the DNA content and morphometric features of the neoplastic cells of the tall cell variant were measured and compared with measurements obtained from neoplastic cells of the usual form of papillary carcinoma. Six of the 11 tall cell neoplasms were aneuploid, as were four of the eight usual papillary neoplasms. Although benign cells were separated from malignant cells in each case, differences between tall and usual papillary carcinoma cells were not observed regarding DNA content, chromatin texture, or nuclear size and shape. Differences in the clinical behavior of these neoplasms will likely need to be explained on the basis of other characteristics.