Outbreaks of a disease in two budgerigar aviaries caused 20% and 53% mortality respectively in recently hatched chicks during the 1985 breeding season. Clinical signs were first observed at 5 to 7 days of age. In most birds darkening of the normal skin colour was followed by death in 2 to 10 days. In individual nests all or part of a hatch could be affected. Occasional survivors had abnormal plumage. Few gross lesions were found at post-mortem examination. Histologically, many large basophilic intranuclear inclusions were present in multifocal degenerative lesions throughout the epidermis, kidney, heart, brain and other tissues. These inclusions were shown by transmission electron microscopy to contain numerous virus particles which, on direct examination, had a .diameter of 46 to 56 nm and a papovavirus-like morphology. These outbreaks were considered to be cases of budgerigar fledgling disease, a syndrome that has been reported in other countries but not previously described in Great Britain.