The incidence of oncocytic neoplasm (Hurthle cell neoplasm—HCN) varies between 3% and 10% in all thyroid nodules. These neoplasms have been classified into oncocytic adenoma (Hurthle cell adenoma—HCA) and oncocytic carcinoma of the thyroid (Hurthle cell carcinoma—HCC). One of the fundamental obstacles to expedited treatment is the inability to establish the diagnosis of HCC preoperatively, either radiologically or with cytology based on fine needle aspiration. This chapter discusses the studies evaluating demographic, clinicopathological (cytology and histology), sonographic, and laboratory criteria in oncocytic/Hurthle cell neoplasms. In addition, it addresses the factors proposed for discriminating oncocytic adenoma (Hurthle cell adenoma) from oncocytic carcinoma (Hurthle cell carcinoma), including molecular biology and immunohistochemistry. Lastly, this chapter explores stratification of oncocytic carcinoma (Hurthle cell carcinoma) risk.