This retrospective analysis aimed to assess hematopoietic and immune recovery in a cohort of 53 patients [males: n = 33; median age: 59 yr (range: 22–70)] who received a FB2 (fludarabine 120–150 mg/m² + IV busulfan 6.4 mg/kg + antithymocyte globulin thymoglobulin 5 mg/kg) reduced-intensity conditioning (RIC) allo-stem cells transplantations (SCT). With a median follow-up of 19 months (range: 2–53), the 2-yr overall survival, disease-free survival (DFS), relapse incidence, and non-relapse mortality were 63%, 59.5%, 35%, and 6%, respectively. In univariate analysis, the factors correlated with a significantly higher 2-yr OS and DFS were a higher total circulating lymphocytes count at transplant (>730/mm3; OS: 81% vs. 43%, P = 0.02; DFS: 73% vs. 45.5%, P = 0.03) and a higher recovery of leukocytes (>5300/mm3) (2-yr OS: 81% vs. 44%, P = 0.007; 2-yr DFS: 72% vs. 46%, P = 0.08), neutrophils (>3200/mm3) (2-yr OS: 76% vs. 50%, P = 0.03; 2-yr DFS: 67% vs. 52.0%, P = 0.1), and monocytes (>590/mm3; 2-yr OS: 80% vs. 45%, P = 0.004; 2-yr DFS: 76% vs. 42%, P = 0.01) at day +30 post-transplant. In multivariate analysis, the only independent factors associated with a significantly higher OS and DFS were a better immune status at transplant (lymphocytes count >730/mm3) and a higher monocytes count (>590/mm3) at day +30 post-transplant. These results suggest that immune status and hematopoietic recovery before and after FB2 RIC allo-SCT can be significant predictors of outcome. This paves the way for future studies aiming to closely monitor the kinetics of immune recovery after RIC allo-SCT and to evaluate the impact of growth factors and other immunostimulatory cytokines in the setting of RIC allo-SCT.