Abstract Over the past 15 years, significant progress has been achieved in our understanding of Lower Palaeozoic radiolarian faunas. However, description of biogeographical patterns of Ordovician Radiolaria is hampered by the paucity of known occurrences as well as possible taphonomic influences. The distribution of all known assemblages is analysed in time and space. Lower Ordovician (especially Tremadocian) Radiolaria are known from two distinct tropical localities of Laurentia. Geographical coverage is much better for the Middle Ordovician (Darriwilian). However, data are concentrated in tropical palaeolatitudes (between 30°N and 30°S). The absence of data from mid/high-latitude localities limits any biogeographical insights. In addition to this there are taphonomic and taxonomic biases. Data are also sparse for the Upper Ordovician. However, comparison between Australian and Nevadan material of Katian age shows strong similarities, suggesting the presence of a coherent tropical radiolarian bioprovince, as in the modern ocean.