As the use of nanomaterials continues to flourish in industrial and biomedical applications so does the concern that these materials may have unanticipated and undesirable effects on human health and the environment. Inhaled or ingested nanoparticles have been detected in the brain, among other organs, raising the question as to their effect on neuronal viability. The effects of multi-walled carbon nanotubes (MWCNTs) on the viability of NeuroScreen-1 (NS-1) cells, a neuronal cell model, were studied. Resazurin reduction and in situ Hoechst and propidium iodide (PI) double staining indicated MWCNTs reduce cell viability. Caspase 3/7 activity on par with etoposide-induced apoptosis was not observed until 72 hours and was only 20-30% higher than controls. However, increased levels of annexin V in the outer leaflet of the cell plasma membranes after 24 hours and a minimum two-fold increase in relative mitochondrial depolarization after 48 hours both suggested MWCNTs promoted apoptosis in this neuronal cell model.