The dramatic rise in the development and application of graphene related materials (graphene, graphene oxide and reduced graphene oxide) as well as of nanosized layered transition metal dichalcogenides gives a strong incentive to study the toxicity of these nanomaterials. It was found that size, surface area, shape, number of layers and amount and type of oxygen containing groups strongly influence toxicity of the nanomaterials. Important toxicity studies are reviewed here with a focus on the above mentioned materials.