Landfills are among the most affordable and acceptable methods in terms of public health and environmental protection for the final disposal of solid waste. Leachate treatment incorporated into anaerobic domestic wastewater systems could be a viable and efficient alternative which would allow minimizing implementation and operation costs of the landfill, to reduce requirements of chemical inputs such as pH conditioners and phosphorus supply. This study showed the potential of anaerobic treatment in an UASB reactor treating a combination of domestic wastewater and leachate in a 5% volumetric ratio of leachate. Under these conditions the reactor assimilated properly the leachate fraction incorporated. With a HRT of 8 h and a mean volumetric organic load of 2.84 kg m−3 d−1 COD removal efficiencies around 70% were obtained, without inhibition problems; however, the necessity of a complementary treatment for improving carbonaceous and nitrogenous organic matter reduction is evident.