Emissions of N2O were measured during the incineration of sewage sludges, originating from various municipal waste-water treatment plants, in stationary and circulating fluidised-bed combustors. The mechanically de-watered sludges had a solids content of 20-30% wt dm, and the pre-dried sludges had 87-94% wt dm. Bituminous and brown coals were also investigated, for purposes of comparison. Measurements from both combustors showed that the sludges yield much higher N2O than the coals, in comparable combustion conditions. Wet sludges emitted higher N2O than pre-dried sludges. Staged combustion proved effective for lowering the emissions of N2O during the combustion of the pre-dried sludge. Increasing the freeboard temperature was shown to be the most effective way of reducing N2O.