BACKGROUND: Multiple endocrine neoplasia 2B (MEN2B) has a classic childhood phenotypic presentation characterized by mucosal neuromas and marfanoid habitus. However, the diagnosis of MEN2B is often delayed beyond childhood, at which time medullary thyroid carcinoma (MTC) may be regionally advanced or metastatic. We examined the extent of this delay and its impact on the treatment of MTC. METHODS: Patients in the MEN database were retrospectively analyzed to determine the age at first presentation for a MEN2B-related complaint and the subsequent time to correct diagnosis. Operative and pathology reports were reviewed to determine the extent of thyroidectomy and cervical lymphadenectomy during the initial and subsequent neck operations. RESULTS: We identified 22 patients with MEN2B, 20 were de novo cases and a M918T RET gene mutation was confirmed in 18 of the 22 patients. Median age at diagnosis of MTC was 13 years (range 6-25 years). The median delay in diagnosis was 26 months (range 0-18 years). Persistent local-regional MTC was present following the initial cervical operation in 12 of 22 patients (55%); including 4 of 13 with MEN2B diagnosed prior to initial surgery and 8 of 9 with MEN2B diagnosed after initial surgery. CONCLUSIONS: Most patients displayed phenotypic characteristics of MEN2B long before the correct diagnosis was made. Half of the patients failed to undergo complete resection of MTC at their initial thyroid surgery. Early recognition of the MEN2B phenotype with a thoughtful approach to preoperative staging and surgery will maximize control of MTC and minimize the need for reoperation.