It is traditional in the British Isles to house the working boar as an individual and this practice was the sensible policy when breeding pig herds were small and replacement boars were purchased singly. However in large herds today several boars are often purchased simultaneously, creating the possibility for group housing during their working life. Important beneficial effects of social contact of young boars up to puberty in terms of sexual behaviour and socialisation have been demonstrated. D'Arcy (1984) found that boars penned singly relative to those in groups of 8 from 30 to 240 kg liveweight took 11 days longer to first successful mount and ejaculation, had a higher number of incorrect mounts and did much more fighting with oestrus gilts. Thus group housed boars were less aggressive to oestrus gilts, had better mating dexterity and had higher mating scores at an earlier age. In addition there may be benefits in terms of comfort and welfare including leg soundness in boars by group relative to individual housing (Tonn et al, 1985; Hemsworth and Findlay, 1978) because of the increased exercise in a group due to the larger area to move in the physical interactions occurring within the group. However, there are concerns about aggressive and sodomy behaviour of mature boars kept in groups as well as the possiblitiy of increased handling difficulties. These latter aspects were studied in group housed boars in this investigation.