On August 8, 2007, the European Commission (EC) released the scientific opinion of the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) on the appropriateness of the risk assessment methodology in accordance with the European Union’s (EU) technical guidance documents for new and existing substances for assessing the risks of nanomaterials. SCENIHR concluded that modifications to the existing technical guidance documents are necessary because special characterization of nanomaterial properties, which potentially differ considerably from conventional chemicals, is needed. Furthermore, the toxicological behavior and effects on health and the environment need to be assessed properly. The opinion states that, due to the lack of common rules for the toxicology of nanomaterials, the risk assessment of nanomaterials should be done on a case-by-case basis. SCENIHR identified issues requiring improvements in the technical guidance and methodologies, and proposed a staged strategy for the risk assessment of nanomaterials. Special consideration is required for the assessment of the potential translocation of nanoparticles in humans and other species, and potential adverse effects, for example, within the cardiovascular system or following passage across the blood-brain barrier.