The thelodont fauna of the Sund vollen Formation (upper Silurian) of Ringerike is described. Several horizons throughout this formation have yielded thelodont scales which are of Baltic and Scottish type unlike those in the English Silurian. Additional information on the thelodonts from the 9g beds is also given. Sedimentological study has enabled an environmental interpretation to be made and compared with that of the well-known Rudstangen fauna. The vertebrates from this latter locality lived in a marginal marine, probably lagoonal environment whilst the thelodonts described here lived in a more open marine environment, probably on a sub-tidal platform. The succession in the Ringerike area from the 9g beds to the top of the Sundvollen Formation is thought to range from upper Wenlock to Iower or middle Ludlow age.