Disease activity in SLE can be difficult to measure and there is no biomarker that uniformly reflects disease activity. There are various disease activity scores, but there is no gold standard assessment tool. This is a review of the development of the BILAG index from the classic BILAG disease activity index to the BILAG-2004 disease activity index and composite response criteria. The original classic BILAG index was revised and distinguished nine organs/systems. Features that indicated damage, such as avascular necrosis, were excluded. There was improvement in the glossary, scoring system and software. The BILAG-2004 index has been shown to be reliable, valid and sensitive to change. The BILAG-2004 index has been modified for pregnancy and has also been used in paediatrics. The SLE Responder Index (SRI) and the BILAG-based combined lupus assessment (BICLA) are composite responder indices incorporating the BILAG index. Since the initial development of the BILAG index in 1984, major improvements have been made in the measurement of disease activity in lupus. However, the BILAG-2004 index is the only transitional index that grades clinical features as being new, the same, worse or improving and incorporates severity in the scoring.