This Guidance addresses the use of nanomaterials in medical devices and provides information for risk assessors regarding specific aspects that need to be considered in the safety evaluation of nanomaterials. According to the EU Recommendation for the definition of a nanomaterial (Commission Recommendation 2011/696/EU, EC 2011) any particulate substance with at least one dimension in the size range between 1 and 100 nm is considered a nanomaterial.