A numerical format for recording details of the main identifying features of cetaceans seen at sea is given. Each identifying character is divided into a number of character states which are coded numerically. This coded format is intended primarily for recording details of cetacean sightings by observers who are not experienced in cetacean identification, including those sightings for which a positive identification is impossible. This should minimise the risk of incorrect identifications and loss of potentially useful data incorporated in such sightings, as well as facilitate the subsequent retrieval of such data for use in broad analyses of the trends in cetacean distribution and abundance. The format designed here for the southern Indian Ocean and is applied to a series of 34 observations made in that area during March and April 1976. The most frequently recorded species was the sperm whale Physeter catodon, which was distributed between 25° and 40°S. New distributional data are reported for the common pilot whale Globicephala melaena and Wilson’s hourglass dolphin Lagenorhynchus cruciger. A possible record of the spectacled porpoise Phocoena dioptrica is noted.