A prognostic factor for patients with acute or subacute idiopathic interstitial pneumonias (IIPs) or acute exacerbation (AE) of collagen vascular diseases-related interstitial pneumonia (CVD-IP) has not been established. We aimed to determine whether the Charlson comorbidity index (CCI) could serve as a prognostic factor for patients with these patients.We assessed baseline prognostic factors among patients with acute or subacute IIPs and AE of CVD-IP who were admitted to hospital between January 2014 and December 2017. We classified them as survivors and non-survivors at 3 months and compared their age, sex, CCI, blood parameters [lactate dehydrogenase (LDH), surfactant protein (SP)-D, Krebs von den Lungen-6, and partial pressure of oxygen in arterial blood/fraction of the inspiratory oxygen], high resolution CT (HRCT) scores and treatment.Sixty eight patients with (mean age, 75 years), were assessed. All patients received steroid pulse therapy. We found that 45 of acute or subacute IIPs and 16 of AE of CVD-IP were included. Stepwise multivariate analysis selected CCI (OR, 1.306; 95% CI, 1.090-1.573; P=0.004), serum LDH (OR, 1.003; 95% CI, 1.001-1.005; P=0.002), and sex (OR, 8.555; 95% CI, 1.729-154.978; P=0.038) as significant predictors of 3-month mortality among these patients. Three-month mortality was significantly worse among patients with high (≥4) than low (<4) CCI (mortality rates: 63.2% 16.3%, P<0.001). Moreover, the composite scoring system including CCI, serum LDH, and sex was acceptable (Bootstrap AUC, 0.859; Bootstrap C-index, 0.747).The composite scoring system including CCI, sex, and serum LDH could be a useful mortality prediction tool for patients with acute or subacute IIPs and AE of CVD-IP requiring steroid pulse therapy.