Background: In the presence of a mutation of the RET proto-oncogene, hereditary medullary thyroid carcinoma may develop already during childhood. Affected children can be cured from this early metastasising disease by prophylactic thyroidectomy. Methodes: To weigh up the chance of a curative operation against the morbidity, and to develop a therapeutic concept, a retrospective analysis of 100 patients with RET mutations, operated on between August 1994 and July 2001, was performed. Results: Patients were divided into those who underwent prophylactic surgery, primary (non-prophylactic) and recurrent surgery and considerable differences were found. Depending on the youngest age of onset for one specific RET mutation, various risk groups were defined: preschool, adolescents, adults, and seniors. At this age, a high chance of biochemical cure can be expected following surgery. Discussion: Whereas nodal positive patients should undergo immediate operation, surgery in nodal negative patients with normal calcitonin levels may be postponed until the age of that particular risk group is reached. A regular monitoring of the calcitonin level is mandatory in these cases.