Stone chewing is a common behaviour in outdoor sows, but its effects on their teeth and stomachs have not been investigated. Tooth wear and damage was assessed by examining the heads of 58 sows culled from outdoor units and 23 culled from indoor units. Tooth damage was found in 28 per cent of outdoor and 30 per cent of the indoor sows, and tooth wear affected 88 per cent of the outdoor and 91 per cent of the indoor sows. The outdoor sows were more prone to wear on the lower molars and premolars, a pattern of wear associated with stone chewing. The stomachs of 152 outdoor sows and 47 indoor sows were examined. Stones were found in 59 of the outdoor sows but in none of those kept indoors. There was no evidence that the presence of stones damaged the stomach, or that stone chewing affected the health of the sows. The teeth of the outdoor sows were worn, but probably not sufficiently to affect their ability to eat during their relatively short productive lives.