Involvement of regional lymph nodes is extremely common in medullary carcinoma of the thyroid gland (MTC). The aim of the present study was to determinate the prognostic of MTC correlated with the regional lymph node involvement. From 1975 to 1994, 23 MTC patients were treated. The surgical protocol included a total thyroidectomy with bilateral dissection of the jugulocarotid chain and of the paratracheal groove. We have distinguished two groups: group N+ (histological lymph nodes involvement) and group N- (absence of histological lymph nodes involvement). In each group we have evaluated the prognostic significance of age, sex, palpable lymph nodes, histological capsular effraction and presence of distant metastasis. The data were analyzed with the exact Fisher test and comparisons by Student t test. Significance was defined as p > 0.05. Survical curves were based on the method of Kaplan Meier. In Group N+ (n = 15), 9/15 patients died: they had palpable lymph nodes, histological capsular effraction and distant synchronous or metachronous metastasis. The median survival was 8 months, when patients have distant metastasis. Six patients are alive, 2 with an elevated thyrocalcitonin level without metastasis, and 3 with resection of metastatic MCT to regional lymph nodes. In groupe N- (n = 8), all patients are alive: 2/8 patients had palpable lymph nodes, 1/8 had histological capsular effraction, but none had distant metastasis. 2 patients underwent resection of regional lymph metastasis and one of pulmonary metachronous metastasis. Gender did not appear to affect the lymph involvement. Factors significantly associated in the group N+ included the following: age (p = 0.003), palpable lymph nodes (p = 0.015), capsular effraction (p > 0.00025), distant synchronous metastasis (p < 0.013). The regional lymph node metastasis had significant influence on the 5-year survival, 48% vs 100% (p = 0.006), and on disease free survival, 16.6% vs 62.5% (p = 0.018). The median time from resection of the primary tumor to the development of metastasis disease was 37 months for patients N+ vs 169 months for patients N-. Involvement lymph node did not affect the metastasis disease, regional involvement or distant metastasis (p > 0.05).