This risk assessment on carbon tetrachloride was carried out specifically for the marine environment, according to the methodology laid down in the European Union (EU) risk assessment Regulation (1488/94) and the Technical Guidance Documents for New and Existing Substances (TGD, 1996). The Montreal Protocol on ozone depleting substances scheduled a phase-out of carbon tetrachloride except for some essential and feedstock uses. This study consisted of the collection and evaluation of data on effects and environmental concentrations from analytical monitoring programs in large rivers and estuaries in the North Sea area. The risk is indicated by the ratio of the Predicted Exposure Concentration (PEC) and the Predicted No-Effect Concentration (PNEC) for the marine aquatic environment. In total 16 studies for fish, 7 studies for invertebrates and 5 for algae have been evaluated. The appropriate assessment factor has been used to calculate a PNEC of 7 microg/l based on long-term exposure for three trophic levels. For coastal waters and estuaries a typical and worst case PEC of 0.003 and 0.31 microg/l are derived. For river waters a typical and worst case PEC of 0.02 and 0.12 microg/l are derived, respectively. These ratios, which do not take into account any dilution within the sea, correspond to safety margins from 25 to 2500 between the aquatic effect and the exposure concentration. Carbon tetrachloride does not meet the criteria of 'toxic, persistent and liable to bioaccumulate' substances as mentioned by the Oslo and Paris Conventions for the Prevention of Marine Pollution (OSPAR-DYNAMEC). It can be concluded that the present use of carbon tetrachloride does not present a risk to the marine aquatic environment.