Diagnostic investigations in a large commercial flock of geese with a history of increased losses and runting, lead to the negative contrast electron microscopic detection of circovirus-like viruses in the lymphoreticular tissue in eight of nine selected geese with growth retardation. With the exception of a mild cloudiness of some air sacs, macroscopic changes pointing to an infection were missed. Histopathological changes concentrated on the lymphoreticular tissue. Lymphocytic depletion and histiocytosis were most evident in the bursa of Fabricius. Basophilic globular inclusions were found in the cytoplasm of medullar and cortical bursal follicular cells, and bursal epithelial cells. Ultrastructural examination of these inclusions revealed paracrystalline or multilayered arrays, or randomly arranged complexes of isometric viral particles, about 14 nm in diameter. The pathological appearence of this, so far unknown, infection in geese shows numerous similarities to circovirus infection in pigeons. In the described flock of geese, a virus-induced immunosuppression could have been a predisposing factor for other infectious agents such as Riemerella anatipestifer or Aspergillus fumigatus, thus contributing to the increased losses and developmental disorders.