The adequacy of gestation stalls to accommodate the postural behaviour of sows is an important welfare concern. The behaviour of 184 sows from parity 0 to 9 was studied in stalls of four widths (55, 60, 65, and 70 cm). Postures, frequency of posture changes, contact with the stall and udder extension beyond the stall were observed for 24 h at 4 and 14 wk of gestation. Injuries were assessed based on number and severity at four 5-wk intervals. Sows spent less time standing and more time sitting in the narrower compared with wider stalls (P < 0.05). The proportion of lying time spent in lateral recumbancy was greater for larger than for smaller sows (P < 0.05) and larger sows made fewer postural changes (P < 0.05). The proportion of sows touching both sides of the stall, or with their udder extending into the adjacent stall, was affected by the interaction of stall width and sow size. Sows rarely touched both sides of the stall, nor did their udders extend into the adjacent stall, when the ratio of stall width (cm) to BW0.33 (kg) exceeded 10.7. Neither stall width nor sow size affected injury scores during the gestation cycle. Key words: Pigs, behaviour, gestating sow, gestation stall, width, body size