In young pigs, it is common to find individuals which grow appreciably slower than their litter-mates. Such “runts” are an important cause of economic loss in the pig industry. Extreme examples are easily recognisable but an adequate definition of what constitutes a runt is more difficult. It is, however, possible to separate slow growing pigs from the remainder and compare them in a number of ways. During the course of a study involving routine observations on the behaviour and growth of piglets, data were obtained which made it possible to compare slow growing pigs with others. It is the aim of this study to tabulate these differences and to relate them to the weights of piglets at birth.