The influence of coccidia on starling nestlings was analyzed. Isospora sp. was found in 67% of starling broods. Although some broods were heavily infected with Isospora sp., nestlings from most infected nests were on average heavier and had longer wings than nestlings from low infection and non-infected nests. Apparently, nestlings that were better fed, had also greater chance of being infected with Isospora sp. These results suggest that coccidia affect the growth of starling nestlings and, although not pathogenic, may affect the reproductive success of starlings, especially when the parental feeding effort could not be sustained.