Rationale: In the absence of a surgical lung biopsy, patients diagnosed with idiopathic pulmonary fibrosis (IPF) in clinical practice could participate in the INPULSIS trials of nintedanib if they had honeycombing and/or traction bronchiectasis plus reticulation, without atypical features of usual interstitial pneumonia (UIP), on high-resolution computed tomography (HRCT). Thus, the patients in these trials represented patients with definite UIP and a large subgroup of patients with possible UIP. Objectives: To investigate the potential impact of diagnostic subgroups on the progression of IPF and the effect of nintedanib. Method's: We conducted a post hoc subgroup analysis of patients with honeycombing on HRCT and/or confirmation of UIP by biopsy versus patients without either, using pooled data from the INPULSIS trials. Measurements and Main Results: Seven hundred twenty-three (68.1%) patients had honeycombing and/or biopsy, and 338 (31.9%) patients had no honeycombing or biopsy. In these subgroups, respectively, the adjusted annual rate of decline in FVC in patients treated with placebo was -225.7 and -221.0 ml/yr, and the nintedanib versus placebo difference in the adjusted annual rate of decline in FVC was 117.0 ml/yr (95% confidence interval, 76.3-157.8) and 98.9 ml/yr (95% confidence interval, 36.4-161.5). There was no significant treatment-by-subgroup interaction (P = 0.8139). Adverse events were similar between the subgroups. Conclusions: Patients with IPF diagnosed in clinical practice who had possible UIP with traction bronchiectasis on HRCT and had not undergone surgical lung biopsy had disease that progressed in a similar way, and responded similarly to nintedanib, to that of patients with honeycombing on HRCT and/or confirmation of UIP by biopsy.