Despite many studies investigating oncocytic (Hurthle cell) lesions in general and oncocytic (Hurthle cell) neoplasms in particular, only few facts are established while uncertainties still obscure much of the disease spectrum. Further research, with implementation of advanced diagnostic aids and conduction of retrospective single or multicenter studies, population studies, and prospective randomized controlled clinical trials is needed to fix its riddle. Knowledge of new pathological entities and ways to differentiate benign versus malignant neoplasms will help clinicians to apply modern diagnostic studies and provide adequate management of this rare cancer. More genetic mutations of oncocytic (Hurthle cell) carcinoma will be discovered in the future. This chapter summarizes the controversies related to neoplastic and nonneoplastic oncocytic (Hurthle cell) lesions, regarding nomenclature, cell of origin, pathogenesis, cytology, histopathology, diagnosis, management, and prognosis.