Background The purpose of our study is to evaluate risk factors for the development of pulmonary fibrosis in the baseline computed tomography (CT) during the course of chemotherapy‐induced pneumonitis (CIP). Methods We retrospectively identified 80 cases of CIP by clinical, radiological, and pathological findings. When fibrosis developed during the follow‐up, the extent of pulmonary fibrosis was evaluated at final follow‐up CT in terms of a 5% volumetric score for six zones. Univariate and multivariate analyses were performed to identify the clinical and radiological risk factors for the development of fibrosis and severe fibrosis over 11% in extent. Results Fibrosis occurred in 26 of the 80 total patients (32.5%) during a mean 5.6 months of follow up. Risk factors for developing fibrosis were revealed as preexisting interstitial lung disease (ILD) and moderate to severe emphysema in multivariate analysis (OR = 10.12, 95% CI = 2.35‐43.66, and OR = 12.85, 95% CI = 2.81‐58.82, respectively). Risk factors for developing severe fibrosis over 11% in extent were revealed as a moderate to severe emphysema (OR = 5.78, 95% CI = 1.07‐31.26) in multivariate analysis. Conclusions Moderate to severe emphysema as well as preexisting ILD visible on baseline CT are risk factors for developing pulmonary fibrosis in the course of CIP. Thin‐section CT may be helpful to predict the risk of pulmonary fibrosis before administering chemotherapy.