Abstract: We investigated allofeeding (feeding of offspring by adults other than their own parents) in the king penguin, Aptenodytes patagonicus, a long-lived pelagic bird that faces severe food shortages during its reproduction and in which parents leave their fasting chick in dense crèches. A 1-year monitoring of 103 breeding pairs and 70 chicks was carried out in a colony in the Crozet Archipelago. We examined whether allofeeding was common enough to alter survival costs or benefits for both the allofed chicks and the allofeeders. Twenty-two per cent of marked adults allofed more than 65% of all the chicks without repeatedly feeding the same chick. Allofeeding in king penguins benefited allofed chicks by increasing their survival, yet little or no fitness cost was detected among allofeeders. We identified proximal factors affecting allofeeding: (1) the breeding conditions of the population were not unusual; (2) allofeeding occurred mostly when parental provisioning was low; (3) alloparents did not respond to increased begging by regurgitating more meals; (4) allofeeders were mostly failed breeders, although successful breeders occasionally allofed; (5) when the colony was no longer organized into breeder territories, allofeeders preferentially fed chicks that had been reared by close neighbours at the time of brooding.