Horses are typically kept in individual housing, such as box stalls, when stabled, but are often run as a group on pasture. This study examined the effects of grouping animals during the stabling period on subsequent social behaviour when pastured in a group. Seven stallions (2-yr-old) were housed in individual stalls, while 12 were housed in groups of 3 for a 9-mon period. Afterwards they were pastured for 6 weeks, with one pasture for the individually housed stallions and one for the grouped housed. The behaviour of the animals in the pasture situation was observed. Thus, only one pasture group was studied for each treatment and results may reflect the group but not be representative of the treatments in general. Previously grouped stallions maintained friendships with their previous group-mates as indicated by their proximity in the pasture. Those that were previously housed individually exhibited more aggressive behaviour, such as bite threats, than did those that had been group-housed. The previously individually housed stallions were more cohesive (remained closer together), and exhibited more social grooming and play behaviour than did the group-housed animals. Stabling as individuals or in groups does have an effect on subsequent social behaviour in group pasture conditions, but some of the effects suggest that the individually housed animals engage in more social activity, perhaps as a re-bound effect.