It is usually accepted that the visual estimation of miss distances at sea is difficult and that it is advisable to employ plotting methods with visual observations (or radar echoes) to assess the positions and movements of neighbouring vessels. Nevertheless, direct visual assessment is likely to remain a useful adjunct to more sophisticated methods, at least under conditions of good visibility, particularly as the use of radar does not absolve the mariner from keeping a good look-out at all times. It seemed, therefore, useful to examine some of the factors involved in the visual estimation of miss distance, in the hope that such an analysis might suggest ways in which the direct assessment of close-quarters situations could be improved.