Data on the distribution of rheophilous aquatic insects from southeastern Australia (including Tasmania) and New Zealand indicate two unusual features in the Tasmanian fauna: there is a higher level of endemism in Tasmania than would be expected—both from its present geographical location with respect to the Australian mainland, and current knowledge of its geological history ‐and a number of rheophilous insects groups which could reasonably have been expected to occur in Tasmania are absent. Possible reasons for these apparent Zoogeographic anomalies are discussed, but none seem entirely satisfactory.