Although nanotechnologies create new and innovative opportunities in many industrial and technological sectors, they present a number of regulatory challenges. There is evidence to suggest that some nanomaterials may pose risks of harm to health and the environment. The nature of these risks, however, is profoundly uncertain. In the first part of this paper, I show that legislative provisions currently used to regulate nanomaterials are ill-equipped for this purpose. In light of this, I proceed in the second part to examine how risks from nanomaterials ought to be regulated. Using what loosely may be described as a cost–benefit analytical framework, I appraise alternative regulatory options and draw initial conclusions about which is likely to prove the most cost-effective.