An epizootic in Canada geese (Branta canadensis) occurred at the Swan Lake National Wildlife Refuge, Chariton County, Missouri, in 1966. Approximately 2,000 geese died during the first 18 days of October. Losses were localized and did not spread to 75,000 other geese on the refuge. Respiratory distress was common among the few sick geese that were observed in the field. All except two geese examined at the laboratory had varying degrees of pulmonary aspergillosis. Three distinct phases of mycotic pneumonia were recorded. A mycosis caused by Aspergillus fumigatus Fresenius, a common mold of soil and compost and a virulent pathogen causing avian aspergillosis, is one of the most common diseases of captive or domesticated birds and mammals. We are not aware of this disease having been reported as an epizootic in wild geese. This paper documents a significant loss from mycotic pneumonia in a migratory population of Canada