Congenital pseudarthrosis is a rare disease with variable clinical effects. The disease remains 1 of the most controversial pediatric entities in terms of etiopathogenesis, therapy, and prognosis. Between 0.5% and 2.2% of patients with neurofibromatosis demonstrate pseudarthrosis in any of the long bones. The exact origin of the lesion is even unclear; although several attempts have been made to determine the type of tissue involving the pseudarthrosis site, only fibrous tissue has been documented in different reports. We present 2 unrelated Mexican patients (male and female) with familial neurofibromatosis and congenital pseudarthrosis of the tibia and fibula. Histochemical and immunostain studies after surgical resection of the affected ends from the pseudarthrosis site of both patients showed a picture compatible with hamartoma. This is the first time when histologic evidence of hamartomatous tissue involving the pseudarthrosis site is presented.