The growing production and use of engineered nanomaterials (NMs) in many applications and the inadequacy of information about the associated health risks mean that it is essential to boost our knowledge of their potential biological effects (at the molecular-cellular and organ-system levels). The production, spread and use of engineered NMs is relatively recent and exposure assessment is complex, so no epidemiological studies or information on their toxicity, particularly on exposed workers, are available yet. Studies to date have been mainly in vitro or on animals - mostly mice. Some have highlighted the potential cytotoxic and genotoxic-oxidative effects of NMs. Most have used high concentrations of NMs and mainly found cytotoxicity. The studies available on the exposure to low concentrations of engineered NMs have detected genotoxic, oxidative and inflammatory effects that may have implications in carcinogenesis; however, there is still much uncertainty, and the results are contrasting. This review examines important cyto-genotoxicity studies on NMs such as multi- and single-walled carbon nanotubes, fullerenes, metal/metal oxide nanoparticles and quantum dots, which are representative of NMs already on the market or about to enter it, and are included in the priority list of manufactured NMs issued by the Organization for Economic Co-operation and Development (OECD). The focus is particularly on studies using experimental conditions similar to occupational exposures, with implications for the health and safety of workers employing, handling and producing NMs.