At its first plenary meeting, held in Krefeld, Germany on 13-14 May 2008, the Decommissioning Cost Estimation Group (DCEG) of the Working Parting on Decommissioning and Dismantling (WPDD) held a topical session on “Risks and uncertainties in decommissioning cost estimates”. This report documents the topical session. The text summarises the main points from the presentations and discussions and includes a summary of the main conclusions from the session.