In hereditary medullary thyroid carcinoma (MTC), recommendations regarding timing and extent of surgery are mainly based on the data of patients with the codon 634 RET mutation, which is the most often affected codon. Little is known about whether these recommendations may also be applied to patients with less common RET mutations. We ascertained the data from 140 patients with FMTC/MEN2A-related RET mutation not affecting codon 634 who have been treated at three specialized centers. The several RET mutations found affected codons 611 (n = 17), 618 (n = 22), 620 (n = 17), 768 (n = 9), 790 (n = 24), 791 (n = 21), 804 (n = 23), and 891 (n = 7). For each codon, the age of the youngest patient with MTC only (41, 7, 18, 29, 13, 47, 20, and 15 years, respectively), MTC with lymph node metastases (46, 24, 21, 34, 46, 47, 50, and 76 years, respectively), and MTC with distant metastases (52, 69, 43, 68, 57, - , - , and 75 years, respectively) was determined. All patients with lymph node metastases had elevated basal calcitonin levels. Based on these data, a more individual recommendation regarding timing and extent of surgery can be given. Because neither gender nor the type of nucleotide substitution for a specific codon appeared to have a significant influence on the age of onset, this recommendation should be based on the affected codon, the age of the patient, and the calcitonin level. Recurrent laryngeal nerve palsy (n = 6) and hypoparathyroidism (n = 3) were rather rare and were found only in patients older than 30 and 43 years, respectively, giving evidence that surgery in young patients can be performed safely.