A study carried out on sewage sludge samples collected at an urban waste-water processing plant located in Zaragoza (Spain) is reported. The concentrations of metals (Cd, Co, Cr, Cu, Ca, K, Fe, Mg, Mn, Ni, Na, Pb and Zn) and agronomic parameters were determined. The speciation of metals based on the sequential extraction scheme proposed by Tessier et al. is reported. Principal component analysis was applied to the results obtained and the correlation factors are discussed. The concentration of heavy metals is lower than that established by European legislation. Heavy metals are mainly associated with the mineral fraction and consequently they show a low availability index.