Tall cell papillary carcinoma (TCPC) and insular carcinoma (IC) are variants of thyroid carcinoma that are considered to be more aggressive than well differentiated papillary or follicular carcinoma. To determine the clinical significance of these diagnoses, we evaluated 65 patients with these tumors. There were 30 TCPCs, 27 ICs, and 8 ICs or TCPCs with focal anaplastic carcinoma (FAC). Forty-two patients (27 TCPCs, 14 ICs, and 1 FAC) are alive and free of disease. Nine patients with IC are alive with distant metastases. Ten patients (2 TCPCs, 2 ICs, and 7 FACs) died of disease. Univariate analysis of disease-free interval determined that, as for all thyroid carcinomas, patient age, tumor size, extrathyroidal extension, and lymph node metastases were significant for prognosis. ICs did significantly worse than TCPCs. Focal anaplastic dedifferentiation predicted a worse prognosis. Multivariate analysis for disease-free interval showed age, number of lymph node metastases, and tumor type to be significant. Analysis of the same factors for prediction of mortality showed that TCPC and IC were not significantly different. These data suggest that TCPC is less aggressive than IC, which often results in disseminated disease. Focal AC predicts poor survival.