Eleven budgerigars (Melopsittacus undulatus) from a zoological collection presented at necropsy with emaciation and splenomegaly or hepatomegaly or both. Polymerase chain reaction assays performed on liver and spleen samples were positive for Chlamydophila psittaci in 2 of 3 birds tested, and histologic findings in 2 additional birds were compatible with chlamydiosis. The aviary was subsequently closed to the public, and a 45-day treatment regimen with doxycycline in the seeds was initiated. No further deaths of birds with hepatomegaly or splenomegaly were observed after the first day of treatment. Further investigation of birds that died during the outbreak with emaciation and with hepatic and splenic enlargement revealed severe necrosis of the spleen and liver suggestive of reovirus infection, which was supported with polymerase chain reaction analysis from paraffin-embedded tissue. This reovirus was sequenced and had 100% homology with a reovirus previously identified in an African grey parrot (Psittacus erithacus). The outbreak did not affect cockatiels (Nymphicus hollandicus) and blue quail (Coturnix chinensis) kept in the same aviary. A group of budgerigars added to the collection soon before the opening of the aviary may have introduced reovirus and Chlamydophila into the collection.