Background: Fibrotic hypersensitivity pneumonitis (fHP) is associated with significant morbidity and mortality. Interstitial lung disease–gender-age-physiology (ILD-GAP) performance in fHP outside the initial cohort was never performed. Aim: To assess the ILD-GAP index’s ability to predict mortality in a Portuguese cohort of patients with fHP and analyse whether other clinical variables add value. Methods: Retrospective analysis of fHP cohort in two Portuguese ILD centres. The baseline ILD-GAP index was calculated. Survival was analysed in months; mortality was the primary outcome. Univariate and multivariate analyses to identify mortality risk factors were performed. Results: A total of 141 patients were included. Fifty-three patients (37.6%) died during the follow-up. The usual interstitial pneumonia (UIP) pattern was found in 49.6%, and their survival was inferior to non-UIP [32 months (interquartile range, IQR = 19, 60) versus 52 months (IQR = 28, 98), p = 0.048]. Patients with an ILD-GAP index higher than three double their risk of mortality [hazard ratio (HR) = 6.48, 95% confidence interval (CI) = (3.03–13.96)] when compared with the patients with an index between 2 and 3 [HR = 3.04, 95% CI = (1.62–5.71)] adjusting for acute exacerbation history. Even though UIP patients had worse survival, it did not reach statistical significance when UIP pattern was added to this model. Acute exacerbation history was an independent risk factor for mortality; however, ILD-GAP still predicted mortality after adjusting for this factor. PaO₂ and 6-minute walk test desaturation were not significant risk factors. Conclusion: ILD-GAP index is a good predictor for mortality in fHP, even after adjusting for other mortality risk factors.