The removal of selected toxic compounds during anaerobic and aerobic digestion of municipal sludge was investigated at pilot scale. The candidate compounds included a mixture of cresols, chlorophenols, heterocyclic nitrogenous compounds, phthalates, and polyaromatic hydrocarbons. A wide range of responses of the candidate compounds was observed in anaerobic digestion with seven compounds removed at efficiencies greater than 90% in primary digestion, four compounds demonstrating removals of greater than 80% after secondary digestion, and five compounds demonstrating overall removals of less than 70%. The secondary digester demonstrated a substantial capacity to attenuate toxics. In aerobic digestion, all of the compounds except the cresols, 2, 4, 5-trichlorophenol, and bis-2-ethylhexylphthalate were essentially eliminated. A dynamic model, developed to predict the fate of toxics during primary sludge digestion, was calibrated with data from the experiments. Biodegradation rate coefficients only could be estimated because of statistical redundancy of the sorption partitioning parameter during the nonlinear regression. The sorption partition coefficients were estimated using octanol–water partitioning coefficients from literature. Key words: anaerobic, aerobic, municipal sludge digestion, toxic organic compounds, biodegradation rate coefficients, model, dynamic.