In a nest of a Northern Goshawk Accipiter gentilis with 3 chicks, north of Groningen city (breeding season of 2000), a male chick showed hyperdactyly with a double tarsometatarsus, each with an accessory claw and two toes. The extra metatarsus was less well developed and was situated on the inner metatarsus. The intertarsal joint had an extra bone. The left tibia was also much shorter (58.3 mm) than the right one (80.0 mm), and the chick was unable to stand at an age of 25 days old. During a post- mortem examination, no malformations were found in the wing structure. Malformations in bill structure were recorded in a full-grown Northern Goshawk embryo; it showed retarded growth of the upper jaw, and a crooked lower jaw. A similar malformation was found in a Common Buzzard Buteo buteo chick (in 2003) of 35 days old; this bird, presumably a female, weighed 840 g (without crop). One month after fledging, it was found dead in the vicinity of the nest.