Information on the diet of the Goshawk Accipiter gentilis during the breeding season was collected in Wales during 1991–1993. Diet consisted mainly of birds (87%) and mammals (13%). Forty-five prey species were collected, ten of which were important in numerical or biomass terms: Feral Pigeon Columba livia, Woodpigeon Columba palumbus, Crow/Rook Corvus coronet Corvus frugilegus, Magpie Pica pica, Jay Garrulus glandarius, Mistle Thrush Turdus viscivorus, Song Thrush Turdus philomelos, Blackbird Turdus merula, Grey Squirrel Sciurus carolinensis and Rabbit Oryctolagus cuniculus. Pigeon biomass was important throughout the breeding season and was more important in the diet of nesting Goshawks on higher ground (>250 m). On lower ground, corvids, mammals and pigeons were the main contributors to the Goshawk diet. Rabbits were more frequently taken at lower nesting territories, and thrushes occurred at all altitudes. Mammals, particularly Grey Squirrel, were found in higher numbers in the diet of Goshawks nesting in small woods (<1000 ha) compared with the diet of Goshawks nesting in two large forests (c. 3500 ha and c. 6100 ha). Goshawks preyed upon juvenile Woodpigeons, corvids and thrushes, and switched from young thrushes to young corvids as the latter became available. Predation peaks on young birds corresponded with the presence of nestling Goshawks in late May to early July. Predation of juvenile prey led to a decrease in mean prey item mass (April-May, 437 g; July, 376 g). No evidence was found to suggest that sexual size dimorphism in Goshawks resulted in partitioning of prey captured during the breeding season. Differences found were probably due to local abundance and vulnerability of prey species rather than specific selection by the two sexes.