The species composition and characteristics of prey consumed by sympatrically breeding Adélie, Chinstrap, and Gentoo penguins were determined by analysis of whole stomachs collected at Point Thomas, King George Island, South Shetland Islands, Antarctica (62°10′S, 58°30′W) during the 1977-1978 breeding season. All three penguins consumed primarily one species of euphausiid, Euphausia superba, although Gentoo Penguins ate significantly more fish, Pleurogramma antarcticum, than either Adélie or Chinstrap penguins. E. crystallorophias, and pelagic and benthic species of amphipods were minor components of the pygoscelid diet. The penguins differed in euphausiid size and in the ratios of male, female, and adolescent euphausiids eaten. These differences were consistent over the entire reproductive cycle. In addition, the species differed in the wet weight of fish consumed by Gentoo Penguins, and in the length of euphausiids consumed by Adélie Penguins. We suggest that these differences in diets are due, in part, to geographical and temporal differences in feeding areas and habitats.