BACKGROUND: Medullary thyroid cancer (MTC) is an infrequent form of thyroid cancer. We aimed to examine how gender and histological characteristics influence the rate of recurrence/persistent disease, distant metastases and survival and also to define specific characteristics of MTC microcarcinomas.METHODS: The medical records of 85 patients with MTC were reviewed. The following characteristics were recorded: year of diagnosis, age at diagnosis, sex, tumor size, number of tumor foci, lymph node metastases, thyroid capsule and vascular invasion, infiltration of thyroid parenchyma and extrathyroid extension, and distant metastases.RESULTS: During follow-up (mean 78.8 months), persistent disease occurred in 40 patients, local recurrences in 5 and distant metastases in 32 patients. Local and distant disease appeared more frequently in patients with larger tumors (p < 0.005) and lymph node metastases (p < 0.01). In addition, patients with invasive tumors had local and distant disease more frequently. The percentage of males who had persistent disease and/or local recurrence was significantly higher than the percentage of males who did not (p < 0.05). Similar results were observed for distant disease (p < 0.01). Independent predictors of recurrence and persistent disease was the presence of lymph node metastases at diagnosis (risk ratio 11.66) and of distant metastases were the presence of lymph node metastases at diagnosis (risk ratio 17.42) and the presence of vascular invasion (risk ratio 2.41). Fifteen patients died due to MTC during follow-up (17.6 %). Patients who died were more frequently males, and had thyroid capsule invasion, extrathyroidal extension, vascular invasion and metastatic disease.CONCLUSIONS: Male sex, tumor size and invasive characteristics of the tumor are negative predictive factors for evolution of MTC.