The use of upflow anaerobic sludge bed (UASB) reactors for sewage treatment was studied in the city of Salta, Argentina. Experiments were performed in two pilot plants. The first pilot plant was a UASB reactor installed after a conventional full- scale sedimentation tank. The second pilot plant was a two-stage UASB system with post-treatment in five waste stabilization ponds (WSP) in series. Both systems studied were highly robust and efficient. They consistently delivered a final effluent in compliance with discharge standards, and produced a small amount of well-stabilized sludge. The performance of the systems was not affected during the coldest period of the year, which lasts about three months. A single-stage UASB reactor followed by a series of WSP could be a very efficient and simple system for the treatment of raw sewage in subtropical regions. More sustainable sanitation requires not only appropriate technologies, but also a fully democratic way of technology selection. Political and economic motivations need to be acknowledged but, at the same time, environmental problems and social injustices must be solved.