Background and Objectives: Angiogenesis is the process of new blood vessel development from preexisting vessel. Angiogenenesis has been considered to be essential for the growth and expansion of a solid tumor. Vascular endothelial growth factor (VEGF), known as one of the most important vascular permeability factors, induces proliferation of endothelial cells, stiumulates angiogenesis, and increases vascular permeability. Several recents reports have documented that VEGF overexpression is associated with poor clinical outcomes in many maligmancies. The aims of this study were to determine whether microvessel density and VEGF expression are related to clinicopathologic factors such as age, sex, tumor size, tumor stage, and prognostic factors and to evaluate the relationship between VEGF expression and angiogenesis in benign and malignant thyroid tumors. Materials and Methods: The subjects were 65 patients (27 with papillary carcinoma, 27 with adenomatous hyperplasia, 11 with follicular adenoma) who underwent thyroidectomy from 1995 to 2001. Imuunohistochemistry was used to detect VEGF expression and microvessel density (MVD) in paraffin-embedded thryoid tumor specimens. Results: The intensity of the VEGF expression did not show stastically difference between benign and malignant thyroid tumors. There was no apparent correlation between VEGF expression and age, tumor size, T stage or scores of the AGES, AMES and MACIS systems. The neo-microvessel density was higher in the maligant tumor than the benign tumors. Also, higher neo-microvessel density was associated with metastases of the lymph nodes and scores of the AMES and AGES systems. Conclusion: Our results suggest that neo-microvessel vessel density may be a significant prognostic factor in the thyroid papillary carcinoma. But the VEGF expression does not appear to be an significant independent prognostic factor for thyroid papillary carcinoma.