Three cases of segmental neurofibromatosis (NF) and one case of bilateral segmental NF are described. Previous cases described as segmental NF are reviewed and evaluated in light of Riccardi's rigid definition of segmental NF. The previously reported cases are then placed in four subgroups. Segmental NF may evolve into a generalized form over time. Also, this disorder may occur in a heritable manner, Genetic counseling of affected individuals must include these facts.