This report represents an attempt to evaluate the potential risks of nuclear ships. Firstly reasons are given why nuclear ship accidents will not lead to accidents of the magnitude of the Chernobyl accident. This is due to much lower content of radioactive material and to different reactor designs. Next a review is given of the types of accidents which have actually occurred. Of these the reactor accidents which may lead to serious consequences for the crew and the environment are considered further. These are reactivity accidents and loss of coolant accidents. In addition the long term risks of sunken nuclear ships and sea disposed reactor compartments etc. are also discussed. Based on available accident data an attempt is made to estimate the probability of serious nuclear ship accidents. (au).