Nanomaterials have the promise of revolutionizing current treatment and diagnosis of diseases, which has led to 33 nanotherapeutics drugs currently on the market and many more in various stages of clinical trials. With an increasing number of products available and in development, along with the unique, emergent properties of the nanoparticle therapeutics themselves, regulatory agencies are now faced with decisions regarding the regulation of such novel technologies. Regulatory guidance, particularly in pre-clinical stages, has the potential to facilitate quick and safe development of these novel materials, but new regulation beyond what is currently in place must be justified in a clear and distinctive toxic response. Herein, we examine literature that compares and correlates in vivo and in vitro nanotoxicity studies to gain a deeper understanding of the modes of nanoparticle toxicity. Additionally, this comparison aims to identify clear and unique toxicity responses caused by nanoparticles, which informs our perspective on pre-clinical nanotherapeutic oversight.