OBJECTIVE To analyze the clinical features and possible prognostic factors involved in the clinical course of a series of 26 patients with the diagnosis of thyroid medullar carcinoma (TMC). METHODS An analysis was made of the variables age, sex, clinical course to diagnosis, paraneoplastic manifestations (flush, diarrhoea), clinical type (sporadic, non-associated, familial MEN IIa associated TMC, familial MEN IIb associated TMC), histologic uni or multicentricity, and stage of disease as possible predictive factors for the evolution. RESULTS The most remarkable prognostic factor was tumoral stage. The likelihood of a patient diagnosed with stage I or II being free of metastatic disease was 1, 0.66 and 0.33 at 15, 16 and 17 years, respectively. In contrast, those patients in stage III at diagnosis had a likelihood of being free from metastasis 5 years after diagnosis and therapy of 0. With regard to sex, a better clinical course was observed among males than among females, statistically significant at 3 and 5, but not at 10 years. No statistical significance was reached with the other possible prognostic factors investigated. CONCLUSIONS Given the obvious influence of tumoral stage of disease on prognosis, an early access to medical attention is desirable for diagnosis and treatment of TMC, as well as an early detection of family cases by a screening test.