In spring 2007 a new aviary for budgerigars (Melopsittacus undulatus) was opened at the Henry Doorly Zoo (Nebraska, USA), and high mortality was observed soon thereafter. Most of the cases were due to trauma, but some animals presented at necropsy with emaciation and hepatosplenomegaly. PCR performed on liver and spleen was positive for Chlamydophila psittaci in two of three birds tested, and histologic findings in two additional birds were supportive of avian chlamydiosis. The aviary was subsequently closed to the public and a 45-day treatment regimen with doxycycline (Doxycycline hyclate, Mutual Pharmaceutical Co., Philadelphia, Pennsylvania 19124, USA) was initiated at 300 mg/kg seed. No further cases of splenomegaly or hepatomegaly were observed after the first day of treatment. In addition, five animals with signs of disease (cachexia, inability to fly) were separated from the main aviary, placed in an indoor cage, and treated with doxycycline at the previously mentioned dose; all animals regained their weight and ability to fly within 45 days. Further investigation of animals that died during the outbreak with emaciation and hepatic and splenic enlargement revealed severe necrosis of the spleen and liver suggestive of reovirus infection, which was supported with PCR analysis from paraffin-embedded tissue. The outbreak did not affect cockatiels (Nymphicus hollandicus) or blue quails (Coturnix chinensis) kept in the same aviary. It is believed that the group of budgerigars added to the collection soon before the opening of the aviary may have introduced reovirus and Chlamydophila into the collection.