Abstract Rationale Familial pulmonary fibrosis (FPF) is defined by two or more family members within the same family being affected by interstitial lung disease (ILD). It has been found that patients with FPF may present earlier and with a more aggressive phenotype than other ILD patients. Patient-reported family history may be used as an adjunct prognostic marker, as patient-reported family history predicts reduced transplant free survival and performs well to identify at-risk individuals, even in the absence of predisposing genetic variants. The objective of this study was to characterize the prevalence, characteristics and prognosis of FPF from a large, multicenter national ILD registry. Methods The Canadian Registry for Pulmonary Fibrosis is a prospective, multicentre ILD registry. All patients with ILD (idiopathic pulmonary fibrosis (IPF), connective tissues disease ILD (CTD-ILD), hypersensitivity pneumonitis (HP), unclassifiable ILD, and other ILDs) were eligible for inclusion. Family history was ascertained by patient questionnaire or physician documentation, kinship was not recorded. In a subset, baseline CT scans were scored for radiologic patterns, blinded to clinical data. Continuous variables are presented as mean ± standard deviation (SD). Death and transplant free survival were evaluated using mixed effects Cox regression model, adjusted for age, sex, smoking, baseline lung function, and treatment. Categorical variables were analyzed using Pearson's chi-square test. Results Of 5454 eligible patients 731 (13%) had patient or physician reported FPF (Table 1). In IPF, HP and unclassifiable ILD, familial versus sporadic ILD was associated with an earlier age at diagnosis. Compared to sporadic IPF, patients with familial IPF were more likely to be female (p<0.001), never smokers (p=0.001) and be referred for lung transplant assessment (p=0.024). Physician reported FPF was associated with increased mortality in adjusted models (HR 1.33, 95%CI 1.09 to 1.62). Of the 1519 participants with radiologic data, 197 (15%) had FPF. Radiologist defined NSIP (p<0.001) and UIP (p=0.014) were more common in FPF compared to sporadic ILD. Conclusions In this multicentre registry, FPF was prevalent in 13% of registry participants and was associated with specific clinical characteristics, including sex, earlier age at diagnosis and a higher likelihood of non-smoking status, and prognosis including mortality. These findings emphasize the importance of ascertaining family history in ILD assessments, as it may offer valuable insights for identifying at-risk individuals and refining management strategies. Further research is warranted to investigate the genetic and environmental factors contributing to FPF and its varied phenotypic presentations.