In a total of 1665 patients with malignant thyroid neoplasms 90 oxyphilic thyroid carcinomas (OTC) were found of whom 55 could be re-examined and newly classified. Morphological and clinical parameters influencing the clinical course were determined. During a mean follow-up period of 6.5 y metastases or local recurrent disease occurred in 12 patients (24%). Apart from 3 early manifestations of metastases, 9 patients developed recurrent disease within, on average, 4.7 y after thyroidectomy: local lymph node metastases and local recurrences occurred within an average of 5.4 y, distant metastases after only 2.7 y. Thyroglobulin proved to be reliable for follow-up with a sensitivity of 88% on levothyroxine and 75% on endogenous TSH-stimulation (specificity: 98%). The frequency of metastases and local recurrences correlated with age at the time of tumor diagnosis, the degree of invasiveness and the local tumor extension (pT4 vs. pT1-3), whereas other factors such as the absolute diameter of the tumor or patient's sex had no influence on the clinical course. The survival probability for 5 and 10 years was 95 and 75%, respectively. All OTC patients should be examined regularly at least once a year by cervical sonography and thyroglobulin measurement. Because 18% recurrences occurred within 4.7 y such examinations should be repeated beyond year 5 after thyroidectomy.