Cerium oxide nanoparticles (nano-CeO2) are included in the OECD priority list of engineered nanomaterials for the assessment of their environmental impact. The present study was carried out in order to assess the nano-CeO2 toxicity to freshwater midge Chironomus riparius larvae at concentrations of 2.5, 25, 250 and 2500 mg of nano-CeO2 per kg of sediment. Experiments were designed to assess the prolonged exposure of midges to nano-CeO2 while adhering to OECD guideline number 218. The following parameters were investigated: nano-CeO2 uptake by the larvae, oxidative stress parameters, the in vivo genotoxic effect and life trait parameters. ICP-MS analysis showed a significant positive correlation between the concentration of nano-CeO2 in the sediment and its uptake by the larvae. No significant mortality was observed in C. riparius and oxidative stress was not detected. The only significantly induced sublethal effect was genotoxicity, which began to manifest at a LOEC concentration of 25 mg kg-1 of sediment and progressively increased at higher concentrations. Therefore, this study indicates that exposure to nano-CeO2 contaminated freshwater sediments does not pose a risk to chironomids at environmentally realistic concentrations. However, significant accumulation of nano-CeO2 by chironomid larvae may pose a risk through trophic transfer to organisms further up in the food chain.