Background <p>Diffuse alveolar hemorrhage (DAH) is characterized by the presence of diffuse ground glass opacities and/or consolidation on chest CT. Emphysema has been reported occasionally. Nevertheless, the pathogenesis, incidence, imaging subtypes, and clinical impact of emphysema in patients with DAH are still unclear.</p> Methods <p>This was a retrospective clinical study. Children with DAH who were admitted to our hospital between January 2013 and December 2019 were included. All chest CT images of the patients were analyzed by two board-certified thoracic radiologists. The clinical features of the patients with diffuse emphysema were further analyzed. A matched case-control study was performed to explore the risk factors for developing diffuse emphysema.</p> Results <p>Ninety-four patients were included. Chest CT scans revealed emphysema in 28 patients (29.8%). Paraseptal emphysema (<i>n</i> = 24) was the most common imaging subtype. The median interval between the onset and development of emphysema was 11.0 months (<i>n</i> = 18, range: 2–113 months). Nine cases developed diffuse emphysema, in which six cases had persistent dyspnea and exercise intolerance, nine cases had persistent ground-glass opacities and 8 cases had a delay in initial treatment of 12 or more months. Compared to <i>t</i>hose in the matched control group, the interval between the onset and start of regular therapy with glucocorticoids was significantly longer in the cases with diffuse emphysema (median interval 13.5 vs. 1.5 months, <i>P</i> &lt; 0.01).</p> Conclusions <p>In cases with DAH, emphysema is a relatively common but ignored radiologic sign and diffuse emphysema seems to be a sign of irreversible lung function impairment. A delay in initial treatment is a risk factor for developing diffuse emphysema.</p>