Purpose: Anaplastic thyroid carcinoma (ATC) is one of the most malignant human neoplasm, with a grave prognosis. This study updates our experience with this unusual neoplasm with specific focus on the response to various treatment modalities. Methods: Forty-seven patients with histologically proven ATC were enrolled (19 men, 28 women; mean age, 62.8 years). This group represented 1.5% of the 3,088 thyroid cancers treated between 1977 to 2002. The mean diameter of tumor was 8.8 cm (range, 2.0∼20.0 cm), and 22 patients had distant metastasis (10 in the lung, 8 lung and bone, 1 brain, 1 mediastinum, and 2 lung and mediastinum). Extrathyroidal extension was seen in 26 (89.7%) of the cases that underwent surgery. Treatment modalities adopted were classified into 5 groups. Group 1, biopsy only; group 2, biopsy and chemoradiotherapy; group 3, debulking only; group 4 debulking and chemoradiotherapy; and group 5, complete excision and chemoradiotherapy. Survival was calculated from the time of diagnosis, and comparisons of survival were done by log-rank analysis. Results: The mean survival was 4.3 months (range, 1.0∼21 months). The mean survival bases of treatment modalities were as follows: group 1 (n=10), 2.1 months (range 1.0∼6.0); group 2 (n=8), 3.6 months (range, 2.0∼7.0 months); group 3 (n=7), 3.0 months (range, 1.0∼11.0 months); group 4 (n=14), 3.5 months (range, 2.0∼9.0 months), group 5 (n=8), 9.4 months (range 5.0∼21.0 months). Conclusion: Even though a small improvement of survival in response was observed with complete excision and aggressive multimodality therapy, nearly all ATC remains ineffective to ongoing treatment modalities and continue to present a therapeutic dilemma. A more effective treatment regimen should be sought for improving the survival rate.