Acute respiratory distress syndrome ARDS is a devastating side effect of a hematopoietic stem cell transplant (HSCT). Recent research has pinpointed pre-transplant risk factors for ARDS after HSCT. This research aimed to identify potential risk factors for post-transplant ARDS after HSCT. The research design was a case-control study within a study. Cases of ARDS were paired with hospitalized controls who did not have ARDS based on age, transplantation type (allogeneic vs. autologous), and time since transplantation. An a priori adjustment was made in a conditional logistic regression model for known risk factors linked with ARDS development and then applied to all other prospective risk factors. About 170 patients hospitalized with ARDS were paired with 177 patients who did not have ARDS. Steroid use before hospital admission was more common among cases (odds ratio [OR] 1.90 [1.13-3.19], P=.02). Cases had a lower platelet count (OR 0.95 [0.91-0.99], P=.02), lower bicarbonate (OR 0.94 [0.88-0.99], P=.035), and higher creatinine (OR 1.91 [1.23-2.94], P=.004) on admission. Patients were more likely to receive a transfusion (odds ratio [95% CI] 2.41 [1.48-3.94], P<.001], opioids (odds ratio [95% CI] 2.94 [1.67-5.18], P<.001], and fluids (odds ratio [95% CI] 1.52 [1.30-1.78], P<.001) within the first 24 hours of admission. Hospitalized patients with ARDS were more likely to have fevers (odds ratio [OR] 1.77 [1.34-2.33], P<.001) and breathe more quickly (odds ratio [OR] 1.52 [1.33-1.74], P<.001). Sepsis (odds ratio [OR] 68.0 [15.2-301.7], P<.001), bloodstream infection (OR] 4.59 [2.46-8.57], P<.001), and pneumonia (OR] 9.76 [5.01-19.00], P<.001) were all significantly associated with ARDS. There are several pre-hospital and early in-hospital predictors of ARDS development in the HSCT group after a transplant. Insights into the mechanisms behind the onset of ARDS can be gained from these results, and risk prediction models tailored to HSCT can be created.