A dual natural infection with psittacine beak and feather disease virus and budgerigar fledgling disease virus in a breeding aviary of budgerigars (Melopsittacus undulatus) is described. One-hundred per cent of newly-hatched birds were affected and mortality was high (85%). Most surviving birds had diarrhoea, feather alterations and 30% mortality after a 5- to 10-week period. Necropsies of 1-week-old and 2-month-old birds demonstrated non-specific lesions, but histologically nuclear inclusions suggestive of viral infection (adenovirus, herpesvirus, polyomavirus) and also cytoplasmic inclusions suggestive of beak and feather disease were seen in integument and internal organs. Staining of tissues with viral specific DNA probes for psittacine beak and feather disease virus and for avian polyomavirus demonstrated simultaneous presence of viral DNA from both viruses in some birds. This is the first description of a concurrent outbreak of psittacine beak and feather disease virus and avian polyomavirus infection in a breeding aviary.