The aim of this study was to assess the main clinical biochemical and immunocytochemical factors influencing survival in 51 patients operated for medullary thyroid carcinoma (MTC). There were 55% of women and 37% of familial cases. Mean age was 43 +/- 3 years. The following survival variables were tested: sex, age, stage, familial disease, Serum Carcino Embryonic Antigen (CEA) and Calcitonin (CT) levels three months postoperatively, intensity of CEA and CT immunostaining, percentage of cells stained for CEA and CT. The actuarial survival rate, including postoperative mortality (N = 1), was studied by uni and multivariate analysis using a Cox model (N = 31). The 5-year survival was 69 +/- 7%. By univariate analysis, stages I or II (p < 0.0001), age of 45 years and less (p < 0.0001), normalized CEA levels (p < 0.006), percentage of CT stained cells greater than 80% (p < 0.04) and weak CT and CEA staining (p < 0.02) were significant predictors of increased survival rates. Age less than 45 and stages I or II were significant prognostic factors of goof survival on multivariate analysis (p < 0.001). We conclude that clinical criteria constitute good survival prognostic factors in patients operated for MTC. The better prognosis of familial cases was probably related to their earlier detection. The prognostic value of immunostaining remains controversial and requires further studies.