The aim of this study was to evaluate the toxicity of sludge produced by wastewater treatment, by using both chemical and ecotoxicological evaluations. Samples of sludge from treatment of urban and industrial wastewater were analysed. Toxicity of sludge was evaluated by measuring Vibrio fischeri, polychlorobyphenyls, polycyclic aromatic hydrocarbons and metals. Results of chemical and ecotoxicological evaluations were found to be discordant. In all samples, contaminants were found to be below the accepted threshold levels; on the contrary, toxicological evaluations of sludge samples obtained from industrial wastewater found these samples to be toxic. These findings indicate that the evaluation of sludge to be used in agriculture should include an ecotoxicological evaluation, as suggested by the European Community in 1999. Furthermore, chemical evaluation of sludge should be performed by using a single method and the chosen method should have the most restrictive threshold levels of all methods currently in use in the EU.