The well being of sows in gestation presents challenges as far as welfare issues are concerned. The inadequate space in gestation stalls could cause stress and discomfort, which might be reflected in postural behaviour. This study assessed the effect of gestation stall size relative to sow size on basic postural behaviour, such as lying, standing, and sitting. Twenty-five sows randomly selected from 4 farms were videotaped for 8 h during the light period. The relationships of duration of postures, time taken for postural changes, and frequency of postural changes with stall size in relation to sow size were analyzed. When the stall length relative to sow length was increased (longer stalls, or shorter sows), sows spent less time standing and took less time to change posture from standing to lying. When the stall width to sow breadth was increased (wider stalls or narrow sows), sows could lie down from standing without stopping at the sitting position during the postural change. If the ease with which a sow in a stall can get up and lie down can be taken as an indicator of sow comfort, the results suggested that the well being of pregnant sows in stalls could be improved by a little increase in the space allowance within the stall.