We have isolated paraspherical viral particles, 60 nm in diameter, from adults of the olive fly (Dacus oleae) collected in Greece. The virus actively replicated in midgut epithelial cells and in advanced infections virions accumulated in microvilli. They were released in the gut lumen and were very abundant in fly faeces. The virions exhibited the salient features of reoviruses, with an external shell and an internal core with a tubular subunit protruding at each vertex of the icosahedron. The viral genome consisted of ten segments of double-stranded RNA totalling 23.4 kbp. Based on its overall properties, this virus can be considered as a nonoccluded insect reovirus.