Following publication of the ALLOZITHRO trial, the FDA released a safety announcement warning that azithromycin should not be given long-term to prevent BOS in patients with a blood or lymph cancer who have undergone allogeneic HSCT. Our site typically initiated azithromycin when patients were diagnosed with BOS post-transplant rather than empirically as prevention. The purpose of our study was to discern whether the use of azithromycin at the time of diagnosis of BOS increased risk of disease relapse in patients who received an allogeneic HSCT for malignant disease. We retrospectively reviewed 432 patients in 3 cohorts: Cohort (1) patients who received greater than or equal to 2 weeks of azithromycin therapy (n = 98); Cohort (2) patients who received azithromycin therapy for less than 2 weeks (n = 63); and Cohort (3) patients who never received azithromycin therapy (n = 271). Neither patients in Cohort 1 (HR 0.44; 95% CI, 0.12-1.53, P = 0.19) nor Cohort 2 (HR 0.66; 95% CI, 0.2-2.19, P = 0.49) were associated with an increased risk of relapse when compared to those who had never received azithromycin. Our data indicate that the prolonged use of azithromycin after allogeneic HSCT is not associated with an increased rate of hematologic relapse.