Weaning piglets at the age of three or four weeks is an integral part of certain production rhythms in modern pig farming. Sorting piglets by weight and mixing them into new groups is a common method in agricultural practice. The aim of this study was to clarify whether the formation of homogeneous weight groups after weaning affects weight development and aggressive behaviour. We compared homogeneous and heterogeneous weight groups and entire litters that were weaned and reared completely. All groups including entire litters were composed of 12 animals. All piglets were weighed the day before weaning, four days later, and on day 38. The number of all aggressive interactions occurring within a group was determined by video analysis for 72 hours after mixing.There during four days after weaning or over the rearing period. Rearing entire litters resulted in significantly higher daily weight gain within four days after weaning and throughout the rearing period. Sorting piglets by weight did not affect the development of weight dispersion in a group. The coefficients of variation of weights in homogeneous and heterogeneous groups which differed significantly at the beginning were on a similar level after 38 days. Neither weight balance of piglet batches at the end of rearing nor growth performance or aggressive interactions were influenced by sorting piglets by weight at weaning.