7098 Background: Allogeneic transplantation of G-CSF-mobilized hematopoietic progenitor cells (HPC) results in rapid and complete engraftment in a large proportion of patients and in relatively fast immune recovery. Methods : We have analyzed by flow cytometry the immune reconstitution in 19 patients (pts) affected by multiple myeloma undergone to allogeneic HPC transplant from HLA-identical related donors after nonmyeloablative conditioning regimen with fludarabine 90 mg/m2 and cyclophosphamide 900 mg/m2. In each patient a comparable number of mononuclear cells, CD3+ T lymphocytes and CD34+ progenitor cells was infused. To evaluate the kinetics of the immune reconstitution, the overall number of total lymphocytes, T, B and NK cells of each patient were assessed before and 1, 2, 3, 6, 12, 18, 24, 30, 36 months after allogeneic HPC transplant. Results: Overall T cell reconstitution was in all the pts at 3 months, since at that time the CD3+ T cell median number was 880 cells/microl (r. 589–1,357). However, in all pts high numbers of CD3+ T cells were achieved at 12 months after transplant (median 1,326 cells/microl, r. 850–2,309). The CD4+ T cell median number was 281 cells/microl (r. 185–433) at 6 months, 391 cells/microl (r. 303–505) at 12 months, 603 cells/microl (r. 433–736) at 18 months. The CD8+ T cell median number was increased from the transplant to 18 months in which it was 1,489 cells/microl (r. 760–1,976). The decrease of CD8+ T cells with the normalization of CD4+/CD8+ ratio was observed at 30 months when CD4+ T cells were 650 cells/microl (r. 370–989) and CD8+ T cells were 690 cells/microl (r. 445–1,743). B cells recovery was observed at 18 months with a median number of 194 cells/microl (r. 40–404). The faster reconstitution was documented for NK cells with a median number of 314 cells/microl (r. 61–647) at 2 months. Conclusions: the complete immune reconstitution in our pts was achieved at 30 months after transplant. Our objective is to evaluate if this slow immune recovery is associated with a high incidence of infectious diseases and a low incidence of chronic GVHD. No significant financial relationships to disclose.