During an inventory of terrestrial isopods in the Ooypolder, east of Nijmegen, The Netherlands, terrestrial isopods infected with Isopod Iridescent Virus (IIV) or Iridovirus were collected. Trichoniscus pusillus was the most important host for Iridovirus; infected individuals and the focus of infection were found mainly between December and March. The symptoms and course of the disease, the route of infection, and the distribution of the virus are discussed. A number of isopod species, Hyloniscus riparius, Trichoniscoides helveticus, T. albidus, Androniscus dentiger, Haplophthalmus mengii, H. danicus, Oniscus asellus, and Porcellio spinicornis are added to the list of species known to be infected with Iridovirus.