We examined the influence of the gas flow-rate, microwave power and trichloroethylene concentration on the destruction of trichloroethylene with a system based on a microwave helium plasma operating at atmospheric pressure. Based on the experimental results obtained, the proposed system allows input concentrations of C(2)HCl(3) in the ppmv range to be reduced to output concentrations in the ppbv range (i.e. virtually quantitative destruction) by using a microwave plasma power below 1000 W. High helium flow-rates and C(2)HCl(3) concentrations allow energy efficiency values above 600 g/kW h to be obtained. Analyses of the output gases by gas chromatography and species present in the plasma by optical emission spectroscopy confirmed the negligible presence of halogen compounds resulting from the destruction of C(2)HCl(3), and that of CCl(4) and C(2)Cl(4) as the sole chlorine species exceeding levels of 30 ppbv. Gaseous by-products consisted mainly of CO(2), NO and N(2)O in addition to Cl(2) traces.