A process for the production of dichlorotrifluoroethane is described. The process comprises reacting perchloroethylene with hydrogen fluoride (HF) at elevated temperature in the vapour phase in at least one reactor in the presence of a fluorination catalyst. The process is operated so that 30 weight % or more of the perchloroethylene reactant that is fed to the at least one reactor remains unreacted having passed through the or each reactor. The dichlorotrifluoroethane may be purified and then used as it is or used to prepare pentafluoroethane.