In this presentation, Virginia A LiVolsi, MD, offers the perspective of a pathologist with more than 30 years experience diagnosing the most severe subtypes of thyroid cancer, including tall cell, columnar, diffuse sclerosis variant, solid variant, hobnail cell variant, micropapillary variant, follicular variant, and anaplastic carcinoma. Dr. LiVolsi describes the unique pathophysiology of each subtype, describes the features that distinguish them diagnostically and provides case studies.