Background: Severe hypogammaglobulinemia was associated with increased mortality during the first year post-transplantation. However, the impact of increasing IgG levels on survival has not been previously evaluated. Methods: In a retrospective cohort, 37 solid organ transplant (SOT) recipients with severe hypogammaglobulinemia (IgG<400mg/dL) were included to determine whether increasing IgG levels to >400mg/dl improved outcomes. Kaplan-Meier analysis were performed to estimate survival, log-rank test to compare survival distributions between groups, Fisher's exact test to determine the association between hypogammaglobulinemia and rejection, graft loss. Results: The median age was 3.8 years (range:0.7-67.3years) at time of severe hypogammaglobulinemia diagnosis. Hypogammaglobulinemia was diagnosed at median of 5.6 months (range:0-291.8months) after transplantation. Types of transplants: livers-small bowel(17); liver-small bowel-kidney(2); liver(5); small bowel(4); liver-kidney(1); kidney/kidney-pancreas(3); heart(3); heart-kidney(1); heart-lung(1). The 3-year survival after the diagnosis of hypogammaglobulinemia was 49.5% (95%CI:32.2-64.6%). Patients were dichotomized based upon IgG level at last follow-up: with IgG>400mg/dL (23patients) and IgG<400 mg/dL (14patients). There was no evidence of a difference in survival (p=0.44), rejection rate during the first year (p=0.44) and graft loss censored for death at one year (p=0.99) between these 2 groups. There was no evidence of a difference in survival between patients who received or not immunoglobulin (p=0.99) or cytomegalovirus hyperimmuneglobulin (p=0.14). Conclusion: Severe hypogammaglobulinemia following SOT is associated with high mortality rates, but increased IgG levels to >400 mg/dL did not translate in better patient or graft survival. DISCLOSURES:Florescu, D.: Grant/Research Support, Behring. Qiu, F.: Grant/Research Support, Behring. Kalil, A.: Grant/Research Support, Behring.