The performance of a pilot stabilization ponds system was evaluated for the treatment of sanitary landfill leachate, focusing on effluent detoxification. Three serial ponds (anaerobic-P1, facultative-P2, and maturation-P3) were evaluated during two different operational conditions: natural condition (period 1) and 24 hours of artificial aeration in P2 (period 2). The ponds system exhibited removal efficiencies of 53% for soluble chemical oxygen demand (SCOD), 81% for filtered biochemical oxygen demand (FBOD), and 84% for NH4+-N during period 1 and 70% for SCOD, 80% for FBOD, and 96% for <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="00539-ilm01.gif"/>-N during period 2. Most metals (Fe, Cu, Cd, Zn, Cr, Ni, and Pb) and organic compounds in the leachate were significantly reduced in the treatment system, with greater reductions during period 2. Moreover, toxicity tests demonstrated the capacity of the system to reduce the toxicity of the raw leachate (up to 89% toxicity reduction).