Epidemiology and prognosis of complications related to allogeneic hematopoietic stem cell transplant (HSCT) recipients requiring admission to intensive care unit (ICU) have not been reassessed precisely in the past few years. We performed a retrospective single-center study on 318 consecutive HSCT patients (2009-2013), analyzing outcome and factors prognostic of ICU admission. Among these patients, 73 were admitted to the ICU. In all, 32 patients (40.3%) died in ICU, 46 at hospital discharge (63%) and 61 (83.6%) 1 year later. Survivors had a significantly lower sequential organ failure assessment (SOFA) score, serum lactate and bilirubin upon ICU admission. Catecholamine support, mechanical ventilation (MV) and/or renal replacement therapy during ICU stay, a delayed organ support and an active graft versus host disease (GvHD) significantly worsen the outcome. By multivariate analysis, the worsening of SOFA score from days 1 to 3, the need for MV and the occurrence of an active GvHD were predictive of mortality. In conclusion, the incidence of HSCT-related complications requiring an admission to an ICU was at 22%, with an ICU mortality rate of 44%, and 84% 1 year later. A degradation of SOFA score at day 3 of ICU, need of MV and occurrence of an active GvHD are main predictive factors of mortality.