Prior to farrowing, 51 multiparous Large White × Landrace sows were housed together with a pen-mate over the peri-parturient period. There were four groups: (1) the pen-mate was unfamiliar and subordinate (n = 12); (2) the pen-mate was unfamiliar and dominant (n = 10); (3) the pen-mate was unfamiliar and subordinate and the farrowing areas were screened (n = 11); (4) the pairs of prepartal sows were well-acquainted (n = 18). As the sows approached farrowing, they became less likely to lie together and more aggressive towards their pen-mates which indicated a preference for isolation. On the day prior to farrowing, the mean number of attacks for the four groups were (1) 22.3, (2) 0.4, (3) 5.0, and (4) 3.9. Aggression was significantly reduced by providing farrowing areas with more isolation and avoidance potential and by penning together during gestation. All the prepartal sows displayed nest building but maternal behaviour was impaired in five sows. The consequences of the results for a group farrowing system are discussed.