Evidence suggests that pigs prefer to associate with their mother and littermates over other group members (e.g. Newberry & Wood-Gush, 1986) and with pigs introduced with them into an established group over resident pigs (Durrell et al., 2000). Few studies, however, have examined whether long-term preferential associations or ‘friendships’ are formed between pairs of pigs within a group. Those studies that have been carried out have either involved observations carried out over extremely limited time periods (e.g. Stookey & Gonyou, 1998) or have simply identified pairs that spend the most time together instead of examining statistically whether some pairs associate significantly more than others (Newberry & Wood-Gush, 1986). The aim of this investigation was to determine whether pairs of pigs form preferential associations, based on statistical analyses of long-term lying partner preferences.