Combustion of fossil fuels is used today worldwide for energy production, but it results in significant release of CO2 in the atmosphere. A net decrease of CO2 emissions can be achieved by the thermal use of regenerative energy sources such as biomass and biomass by-products. Especially co-firing biomass waste and coal, offers a number of technical, economical and environmental benefits in addition to reduced net CO2 emissions, such as conservation of fossil fuel resources, minimisation of waste disposal and reduction of the dependence on fuel imports. Although co-combustion of waste wood with coals is a promising technique, it entails some environmental risks due to the chemical nature of waste wood. Waste wood is usually impregnated with a number of substances, which can result in the release pf toxic compounds like dioxins and furans. Since the early 1950s, pentachlorophenol (PCP) and lindane have been used as wood preservatives, because of their fungicive and insecticide properties. The objectives of this work were to determine the PCDD/F emissions during co-combustion of waste wood and a low grade lignite in an industrial scale combustor, to compare them with emissions from co-combustion of natural wood, and to correlate gas emissions with the fuel mixture properties.