We report here a 48-yr-old woman presenting with a solitary thyroid nodule in the left lobe of the thyroid. The aspiration cytology of the nodule was reported as follicular neoplasia and she underwent surgery. Frozen section was suspicious for medullary thyroid carcinoma and a total thyroidectomy was performed. The pathology report revealed medullary thyroid carcinoma, follicular variant. Immunohistochemical analysis was negative for thyroglobulin and positive for calcitonin. A few patients with this variant have been reported in the literature, mainly diagnosed by immunohistochemical features of the tumor. In light of the limited information we have obtained from the literature, it is reasonable to emphasize that these cases should be distinguished from the mixed medullary-follicular thyroid carcinomas and medullary carcinomas with entrapped follicles. Immunohistochemical examination with calcitonin and thyroglobulin is also essential.