The complement system is involved in several aspects of renal disease, including primary renal diseases, dialysis and renal transplant rejection. Initially, a role for complement in renal disease was inferred solely from the deposition of complement components in affected kidneys and changes in complement levels in the circulation during active disease. Recent studies have shown how complement modulates the onset, development and the resolution of renal disease. Current research provides clues on the role of individual complement components and activation pathways as well as possible modes of complement regulation in the management of renal disease.