This paper presents a study of pollutant emissions during combustion tests of sewage sludge in a pilot fluidized-bed system. Mono-combustion of sludge and its co-combustion with coal were compared with combustion of coal alone. It was verified that the high N content in the sludge did not lead to an increase in NOx production and that air staging gave rise to very low levels of NO emissions. SO2 diminished when the sludge was introduced, but achieving acceptable levels to meet emission limits still required the use of limestone. The emissions of heavy metals were increased during co-combustion but decreased during sludge mono-combustion, with the exception of Hg, which was retained more efficiently in cyclone ashes during co-combustion. The study of the dependence of the Pb and Cd distributions on the diameter of the fly ash emitted showed that these metals were associated with particles with an average diameter of 2-3 mum and that their removal would only be possible with adequate gas cleaning.