Hürthle cell neoplasms of the thyroid gland are uncommon but potentially lethal lesions, the treatment of which is controversial because of a lack of information about their biological and clinical behaviour. Based on histological criteria Hürthle cell tumours cannot always be separated accurately into benign and malignant. Unexpected evolutions with malignant late recurrence of an adenoma previously labelled as benign have been reported. The authors reviewed the clinical and pathological features of 32 patients with Hürthle cell adenomas. The results suggest that total thyroidectomy 'de principe' is not necessary and that some electron microscopy criteria are useful to understand the nature and to predict the biological deportment of Hürthle cell adenomas.