Background: Acute exacerbation of chronic fibrotic idiopathic interstitial pneumonia (AE-IIP) is associated with a high mortality rate. In 2016, the International Working Group classified the etiology of AE-IIP into idiopathic and triggered. Several factors can trigger AE-IIP; however, the triggers associated with the worst prognosis have not been identified. The aim of this study was to investigate the prognosis of patients with various types of AE-IIP, particularly infection-triggered, non-infection-triggered, and idiopathic AE-IIPs. Methods: We retrospectively collected data for 128 patients with chronic fibrotic IIP (CF-IIP) who were hospitalized because of respiratory failure during the period between April 2009 and March 2019 at Juntendo University Hospital. There were 79 patients who developed AE-IIP, and 21 patients who developed bacterial pneumonia combined with CF-IIP. AE-IIP was classified into idiopathic, infection-triggered, and non-infection-triggered. We analyzed differences in patient characteristics, examination findings, and prognosis among the types. Finally, we evaluated risk factors for early death due to AE-IIPs. Results: Idiopathic, infection-triggered, and non-infection-triggered AE-IIPs were diagnosed in 34, 25, and 20 patients, respectively. The survival time was significantly longer for bacterial pneumonia combined with IIP than for AE-IIP. Moreover, the survival time was significantly longer for infection-triggered AE-IIP than for idiopathic or non-infection-triggered AE-IIP. The mortality rate was significantly lower with infection-triggered AEIIP than with other types of AE-IIP. Finally, a multivariate analysis revealed that radiological findings at the time of onset of AE-IIPs and AE-IIP patterns were independent risk factors for early death. Conclusion: Our results suggest that patients with infection-triggered AE-IIP may have a better prognosis than those with other types of AE-IIP.