The high concentration of trivalent chromium along with organic/linorganic compounds in tannery sludge causes severe ground-water contamination in the case of land disposal and chronic air pollution during incineration. In the present investigation the sludge was subjected to starved-air combustion at 800 degrees C, which prevented the conversion of Cr3+ to Cr6+. The efficiency of starved-air combustion was confirmed through differential thermo-gravimetric analysis (DTG), electron spin resonance (ESR) and Fourier transform infrared (FTIR) analysis. The calcined sludge was solidified/stabilized using fly ash, clay, lime and Portland cement as mixture constituents. The solidified specimens were tested for compressive strength and heavy metal fixation. The compressive strength and metal fixation of the calcined sludge (Cs)-fly ash (F)-cement (C) mortar at a ratio of 41.66% Cs, 41.66% F, 16.66% C were 185 kg cm(-2) and 93.84%, respectively. The stabilization of chromium(III) in the cement gel matrix was confirmed with scanning electron microscopy. Leachability studies were carried out to determine the percentage of metal fixation and chemical oxygen demand in the leachate. (c) 2006 Society of Chemical Industry.