Rationale Patients with interstitial lung disease (ILD) are at risk of hospitalisation due to respiratory decompensation. A proportion of ILD-related admissions are secondary to an 'Acute Exacerbation of Interstitial Lung Disease' (AE-ILD) which research defines as <30-day history of progressive symptoms and radiologically new bilateral ground-glass changes on computed tomography (CT). The pathogenesis of AE-ILD remains unclear, but its associated mortality is recognised as significant. By further understanding the role AE-ILD and other admissions play in disease trajectory, clinicians can hope to understand research priorities and provide holistic care to the ILD patient population within appropriate timeframes.Aims To further understand the significance of all ILD-related hospital admissions on disease trajectory.Methods We undertook a multi-centre retrospective observational study of ICD-10 coded primary admissions for interstitial lung disease patients ≥18 years old between 01.01.2017 and 31.12.2019 across seven NHS trusts in the North West of England, with five now completed. The primary outcome was time to death from admission. AE-ILD was identified by review of clinical notes and defined by <30-day progression of symptoms not caused by cardiac, thrombotic or pneumothorax events. Further data on patient demographics, admission investigation results, treatments and mortality were collected from coding and inpatient records.Results 607 admissions across five NHS trusts met inclusion criteria. 40/607 (6.6%) were excluded from analysis due to insufficient data to determine AE-ILD status. Incidence of AE-ILD within our admission cohort was 51.1% (290/567 admissions) and 'other' admissions 48.9% (277/567 admissions), secondary to presentations such as pneumothorax and chronic disease progression. Mean survival of AE-ILD was 400.4 days (95% CI 323.3 - 477.5) and other 764.2 days (95% CI 654.7 - 873.7) with statistically significant difference in survival (p <0.001). Inpatient mortality within the AE-ILD cohort was 22.8% and 90-day mortality 51.4%. Of the AE-ILD cohort, 17.2% saw palliative care specialists during their admission. Subsequent multivariate cox regression analysis of all-cause mortality showed AE-ILD remained a risk factor for mortality (HR 1.34, p = 0.006), alongside idiopathic pulmonary fibrosis diagnosis (HR 1.45 p = 0.045), prior long-term oxygen use (HR 2.07, p <0.001) and increasing number of co-morbidities (HR 1.09, p = 0.013). Conclusions Hospitalisation events related to ILD appear significant with high inpatient and post-admission 90-day mortality. AE-ILD conveys increased risk of mortality in our dataset, even with other variables considered. Further research is needed to understand AE-ILD and potential treatments, alongside improvement of access to holistic and palliative care.