The molecular and enzymatic abnormalities of mitochondria in oxyphilic / oncocytic / Hürthle cells and their respective tumours are reviewed in a series of sections: "Mitochondria, ageing, neurodegenerative diseases and cancer", "Mitochondrial abnormalities in Hürthle cells and Hürthle cells tumours", "Mitochondrion-related alterations in tumours with and without Hürthle cell/oncocytic features", "True and secondary oxyphilia", and "Bcl-2 expression, apoptosis and necrosis in Hürthle cell tumours and tumour-like lesions". The clinicopathological and pathogenetic meaning of the data on record on these topics are discussed, with an emphasis on thyroid pathology.