We studied the American Society for Blood and Marrow Transplantation (ASBMT) 6-month (m) freedom from treatment failure (FFTF) as a predictor of survival for patients with acute GVHD (aGVHD) requiring treatment. Adult patients undergoing allogeneic hematopoietic cell transplant (HCT) from February 2007 to March 2009 who were enrolled in a prospective biomarker clinical trial and developed aGVHD requiring systemic corticosteroids by day +100 were included (N=44). Six-month FFTF was defined as per the ASBMT guidelines (absence of death, malignancy relapse/progression or systemic immunosuppression change within 6 months of starting steroids and before chronic GVHD development). aGVHD was treated with systemic corticosteroids in 44 patients. Day 28 response after steroid initiation (complete response+very good partial response+partial response) occurred in 38 (87%) patients, but only 28 (64%) HCT recipients met the 6-m FFTF end point. Day 28 response predicted 6-m FFTF. Achieving 6-m FFTF was associated with improved 2-year (y) OS (81% vs 48%; P=0.03) and decreased 2-y non-relapse mortality (8% vs 49%; P=0.01). In multivariate analysis, 6-m FFTF continued to predict improved OS (hazard ratio, 0.27; P=0.03). The 6-m FFTF end point measures fixed outcomes, predicts long-term therapeutic success and could be less prone to measurement error than aGVHD clinical response at day 28.