Pigs have been shown to prefer associating with certain groups of pigs over others, for example their mother and littermates over other group members. However, few studies have properly examined whether long-term preferential associations or ‘friendships’ are formed between pairs of pigs within a group. The aim of this study was to determine whether pigs form long-term preferential associations, based on lying partners, and to examine factors that may influence the formation of these associations. Thirty three pigs from 16 litters were housed together from 4 weeks of age. At 10 weeks they were split into groups of 16 and 17 pigs and introduced into the two pens (1st pen). At 17 weeks the two groups swapped pens (2nd pen). The lying patterns of each group were recorded over 3 weeks in the 1st and 2nd pens. The existence of preferential associations was identified in both groups. Of the 33 pigs observed, 32 formed preferential associations with one or more pigs in their groups. These findings suggest that unrelated pigs are capable of forming preferential associations. However, it is unclear whether such associations are widespread or important to pigs, since most dyads’ preferential associations were not consistent between pens.