Surgical therapy of incidentally postoperative diagnosed small sporadic medullary thyroid cancer (MTC) is discussed controversially. In principle completion thyroidectomy with neck dissection and regulary tumor follow-up are under discussion. A total of 277 patients with MTC were treated between 1986 and 2004. In 22 cases diagnosis of a small (pT1 or pT2) sporadic MTC was incidental and only postoperatively confirmed. Normally total thyroidectomy with neck dissection is standard surgical therapy of a known MTC. Because of postoperative incidental diagnosis in all 22 cases surgical therapy was less then total thyroidectomy. Mutation analysis of RET Proto-Oncogen and familial history were negative in all cases. All patients were systematically followed-up in defined intervals by calcitonin, pentagastrin stimulation test, carcinoembryonic antigen and ultrasound. Median follow-up is 6.2 years (range: 2-13 years) and although a hemithyroidectomy or less was performed all 22 patients are cured by the MTC. We conclude that completion thyroidectomy and neck dissection are not mandatory in such patients, if the tumor is completely resected and genetic background is excluded. Indispensably a systematic long term follow-up of at least 10 years, better a life-long, is mandatory.