Nanotechnologies, defined as techniques aimed to conceive, characterize and produce material at the nanometer scale, represent a fully expanding domain, and one can predict without risk that production and utilization of nanomaterials will increase exponentially in the coming years. Applications of nanotechnologies are numerous, in constant development, and their potential use in the medical field as diagnosis and therapeutics tools is very attractive. The size particularity of these nanomaterials gives them novel properties, allowing them to adopt new comportments because of the laws of quantum physics that exist at this scale. However, worries are expressed regarding the exact properties that make these nanomaterials attractive, and questions are raised regarding their potential toxicity, their long-term secondary effects or their biodegradability, particularly when thinking of their use in the (nano)medical field. These questions are justified by the knowledge of the toxic effects of atmospheric pollution micrometric particles on health, and the fear to get an amplification of these effects because of the size of the materials blamed. In this paper, we first expose the sensed medical applications of nanomaterials, and the physicochemical and molecular determinants potentially responsible for nanomaterials biological effects. Finally, we present a synthesis of the actual knowledge regarding toxicological effects of nanomaterials. It is clear that, in regard to the almost empty field of what is known on the subject, theres an urge to better understand biological effects of nanomaterials, which will allow their safe use, in particular in the nanomedicine field.