Nine species of clitambonitoid brachiopods have been described from the Middle and Upper Ordovician of the Oslo Region, Norway. They include, Hemipronites? sp., Clitambonites schmidti, Clinambon anomalus, Ilmarinia dimorpha, Vellamo oandoensis, Kullervo hibernica, Kullervo aff. parva, Kullervo aff. punctata and Kullarvo cf. lacunata. The palaeobiogeography and palaeoecology of the Upper Ordovician clitambonitoid brachiopods are discussed. The species found in the northern and western parts of the Oslo Region are mostly related to those of the Baltic carbonate platform, despite surprisingly large differences in lithology. The foreland basin (the Oslo-Scania confacies belt of Jaanusson & Bergstrøm, 1980) has a different fauna, dominated by pandemic species of Kullervo. This genus is supposed to have developed in parallel in Avalonia (pandemic species and the North American species) and Baltica (all endemic species to Baltica), from an early kullervo of either Baltic or Avalonian origin. The rapid spread of the genus in the North Atlantic area is linked -in time - to the large bentonite in the Middle Caradocian.