The Harvey-Bradshaw Index (HBI) was published in 1980 as a simplified alternative to the more complex Crohn's Disease Activity Index (CDAI), which requires a 7-day patient diary and haematocrit measurement. The HBI uses five clinical variables assessed on a single day: general wellbeing, abdominal pain, stool frequency, abdominal mass, and extra-intestinal complications. HBI score correlates strongly with CDAI and is used in clinical trials, outpatient monitoring, and clinical decision-making. It is particularly useful in UK/European IBD practice where CDAI is less commonly used.