The characteristics of the seven intermediate filament proteins expressed during the development of neurons are reviewed. The most extensively studied have been neurofilament proteins (NFP) and peripherin. The relative plasticity of the peripherin network can account for its possible role during development when the axons of the neurons in which this protein is expressed have to find their targets crossing a non-neural environment probably in answer to signals from this environment and from their respective targets. Peripherin may assume a similar role when axons regenerate. NFP are considered as maintaining the axonal caliber, thus ensuring a normal axonal transport. Their network is highly disrupted in several diseases, particularly in motor neuron diseases. Mice transgenic for human NFP or in which mouse NFP are overexpressed have been obtained and are considered as animal models for these diseases.