The aim of the present study was to explore the diagnostic value of the immunophenotypic analysis of bone marrow mast cells (BMMC) in indolent systemic mast cell disease (SMCD) patients. For that purpose, a total of 10 SMCD patients and 19 healthy controls were analyzed. Our results show that BMMC from SMCD are different from normal BMMC with regard to both their light scatter and immunophenotypic characteristics. Accordingly, forward light scatter (FSC), side (90 degrees) light scatter (SSC), and baseline autofluorescence levels were higher in BMMC from indolent SMCD patients than they were in control subjects. From the immunophenotypic point of view, the most striking findings were the constant expression of CD2 (P = .0001), CD25 (P = .0001), and CD35 (P = .06) molecules by BMMC from SMCD patients, markers that were absent from all normal controls. In contrast, CD71, absent in BMMC from indolent SMCD, was positive in BMMC from normal subjects. Although, slight differences between BMMC from SMCD patients and normal controls were found in several other markers, they did not reach statistical significance. In conclusion, our results show that simultaneous assessment of FSC/SSC and reactivity for the CD117, CD2, CD25, CD33, and CD35 forms the basis for the immunophenotypic characterization of BMMC from SMCD in adults and should be integrated with clinical and morphologic studies for the diagnosis of the disease.