Purpose. The aim of this study was to assess the degree of spermatogenesis defects in sperm analysis in long-term male survivors after allogeneic hematopoietic stem cell transplantation, to identify the risk factors related to potential infertility after hematopoietic stem cell transplantation and to provide data on longitudinal sperm recovery after hematopoietic stem cell transplantation. Design and Methods. The Late Effects Working Party of the European Group for Blood and Marrow Transplantation reported here data of sperm analysis from 224 male who underwent hematopoietic stem cell transplantation. The median time between transplantation and sperm analysis was 63 months (8-275). Results. In the last sperm analysis, presence of any degree of spermatozoa was reported in 70 (31%) and complete azoospermia in 154 (69%) patients. In multivariate analysis, being conditioned with total body irradiation (RR 7.1; 95% CI 3.4-14.8) and age > 25 years at transplantation (RR 2.4; 95% CI 1.09-5.2) were significantly associated with higher risk for azoospermia. In patients not conditioned with total body irradiation, ongoing chronic graft-versus-host disease is the main adverse factor for sperm recovery (RR of 3.11; 95% CI, 1.02-9.47; P=0.045). Conclusions. We found that the already established risk factors like total body irradiation and age older than 25 years at hematopoietic stem cell transplantation are the most relevant adverse risk factor for sperm production after hematopoietic stem cell transplantation. Moreover, for the first time ongoing graft-versus-host disease has resulted the most relevant adverse factor for sperm recovery particularly in patients conditioned without total body irradiation. Here, a useful scoring system to predict the probability of male long-term survivors' azoospermia has been introduced.