Anaplastic carcinomas are the lethal thyroid neoplasms and have poor survival rate and prognosis. Pre existing well differentiated thyroid neoplasms can give rise to anaplastic carcinoma. Here, we report a case of anaplastic carcinoma in a young female in a colloid goitre as an incidental finding diagnosed by histopathological examination. Thyroid function tests showed suppressed TSH and elevated FT4 and FT3. Anti-thyroid hormone drugs were started. Thyrotropin receptor antibody was negative. USG neck showed single hypoechoic lesion in the periphery of the right lobe. A thyroid scan revealed focal hot and cold nodules and fine needle aspiration biopsy (FNAB) of the thyroid gland showed colloid nodule. Patient underwent right side lobectomy and final histopathology showed anaplastic thyroid carcinoma. Our case is interesting from a pathophysiologic perspective, since it suggests that nodular goiter can be associated with an aggressive form of thyroid carcinoma. We would like to emphasize that there should be a high index of suspicion in patients with nodular goiter for careful evaluation to detect any associated cancer.