A pair of northern goshawks (Accipiter gentilis) breeding in a public park in the city center of Hamburg, Germany, raised 12 healthy and five aberrant offspring between 1996 and 2000. Aberrant nestlings (three males and two females) had pale silver-blue plumage and displayed severe locomotor disorders. Histopathologically, the defects were characterized by adendritic feather melanocytes and mild degeneration of the cerebellar white matter. Epidemiologic results were suggestive of a hereditary autosomal recessive defect, which may have originated from close inbreeding during the foundation of Hamburg's urban population of northern goshawks.