The anaerobic process is a very attractive solution for the treatment of highly loaded wastewaters, due to low sludge production and energy consumption; nevertheless, its application to tannery wastewater shows several drawbacks due to the complexity of the chemical composition. The objective of this paper is to summarize recent research efforts in the field of anaerobic treatment of tannery wastewaters. Primary attention is focused on the type of reactor geometry, the filling material and the operational regime. The parameters affecting the removal of the organic matter, the biogas production and the sulfate reduction were also analyzed and compared. Particular attention is then made on how the presence of toxic substances, such as sulfide, affects the performance of the process, and how it affects the synergistic effects of the combined anaerobic and aerobic processes. (C) 2010 Elsevier B.V. All rights reserved.