BACKGROUND: Multiple endocrine neoplasia type 2b (MEN2B) is a rare syndrome characterised by the occurrence of medullary thyroid carcinoma at a young age in all patients, and phaeochromocytoma at a later age in half of the patients. Once a medullary thyroid carcinoma causes symptoms, it has usually already metastasised to the lymph nodes and curative treatment is seldom possible at that stage. CASE DESCRIPTION: We present two patients who had phenotypical characteristics of the MEN2B syndrome from a young age: mucosal neuromas, ptosis, a marfanoid habitus, gastrointestinal problems and crying without tears. When the diagnosis was made, at the ages of 15 and 10 years respectively, both patients had already developed metastatic medullary thyroid carcinoma. CONCLUSION: Early recognition of the phenotype of MEN2B syndrome is crucial in order to be able to perform a prophylactic or curative thyroidectomy. The mucosal neuromas, which are usually present from infancy, are a particularly important characteristic.