<p><?tk 4?>This study assesses the relationship between ANCA-associated vasculitis and immune-mediated inflammatory diseases (IMIDs) in first-degree relatives. People with AAV were matched 1-to-1 with control participants with no IMID in a case control study. Participants were asked whether their first-degree relatives had IMID. The likelihood of a positive family history was compared between cases and controls using conditional logistic regression. Additionally, the risk of first-degree relatives of cases having IMID was explored using generalised estimating equations. 145 AAV cases were matched with 145 controls. A family history of IMID was reported by 46.2% of those with AAV and 16.6% of controls. After adjustment for participant age and number of known family members, AAV cases were seven-times more likely to have a positive family history compared to controls (OR 7.25, 95% C.I. 3.27–16.09). 12% of first-degree relatives of AAV participants had an IMID compared to 3.5% of first-degree relatives of control participants. First-degree relatives of AAV participants were four-times more likely to have an IMID compared to a relative of a control (OR 4.03, 95% C.I. 2.46–6.62). Female first-degree relatives had double the risk of having an IMID, compared to male first-degree relatives. A history of IMID in first-degree family members is associated with an increased chance of a person developing AAV. Conversely, the presence of AAV in a first-degree relative is associated with having an increased chance of having an IMID. This implies a shared familial susceptibility between AAV and these diseases.</p>