To determine variations within and between litters in the weaning process and behavioural development, the behaviour of four focal piglets from each of nine litters was recorded at the ages of 4, 6, 8 and 10 wk in a 12.5-ha semi-natural environment. The piglets were weighed at birth, at 7–11 d and at 7 wk. Activities and nearest-neighbour distances were recorded instantaneously and social interactions continuously during 4 times 11 min/piglet at all ages. Within-litter comparisons were obtained by transforming raw data to standard scores within litters. There were significant age effects on all behavioural variables except aggression, which, however, was very rare. There were also significant effects of sow and boar on several behavioural variables, as well as interactions between sow/boar and age, indicating a possible genetic influence on the behavioural development. Within-litter variations did not relate to sex or weight. Within litters, some individuals tended to be more associated with their families and to rely more on milk for nutrients whereas others tended to affiliate with other families and spend more time feeding on solids. The latter group could be conceived of as piglets starting the weaning process earlier.