Background: Medullary thyroid carcinoma (MTC) accounts for 5 to 10% of all thyroid cancers but is responsible for a disproportionate number of deaths. Methods: We performed a retrospective review to describe clinical outcomes in patients with medullary thyroid carcinoma, screening a subset of patients for somatic mutations in the RET and p18 genes and performing genotype-phenotype correlation in a tertiary-care referral hospital from 1967 to 2009. Results: We studied a total of 94 patients identified from a prospectively maintained thyroid cancer database. Data gathered included patient demographics, serum calcitonin, clinical outcomes, histopathology, genetic analysis, and status at final follow-up. A subset cohort (n = 50) was screened for somatic mutations in the RET gene and the three exons of the p18 gene. The subset cohort was composed of hereditary medullary thyroid carcinoma (HMTC) (n = 19, index patients = 10, screen detected = 9) and sporadic medullary thyroid carcinoma (SMTC) (n = 31). There were no mutations in the p18 gene in the subset cohort. Conclusions: A total of 67 SMTC and 27 (28.7%) HMTC cases identified. SMTC were older at initial presentation (52 vs. 34, P = 0.003), had higher preoperative serum calcitonin levels (7968 vs. 1346 ng/L, P = 0.008), and had lymph node recurrence (P = 0.001) compared to HMTC. The tumors were smaller in HMTC (P = 0.038). Overall 10-year survival in SMTC versus HMTC was 69 versus 93% (P = 0.12). On multivariate analysis, vascular invasion (hazard ratio 6.4, P = 0.019) was an adverse predictor for disease-free survival. HMTC in the era of RET analysis presents with a smaller primary tumor, lower preoperative serum calcitonin levels, and lower rates of lymph node metastasis. Mutations in the p18 gene were not a major factor in medullary thyroid carcinoma tumorigenesis.