This study compares social behavior of infants of resident mothers and infants of immigrant mothers in social groups of the mountain gorilla, Gorilla gorilla beringei. Infants of immigrant mothers spent more time in proximity to their mothers during group resting. They spent more time in solo play and less time in social play during group feeding. Their opportunity for social interaction with peers may be restricted mostly to group rest periods and their social play levels during this time are higher than infants with resident mothers. However, during both group resting and feeding they spent less time near other infants and they initiated fewer dyadic play bouts.