In vitro, Imatinib inhibits the proliferation and stimulates the osteogenic and adipogenic differentiation of mesenchymal stromal cells (MSC). However, it is unknown whether Imatinib affects the biology of MSC in vivo. We asked whether MSC from long-term Imatinib-treated CML patients were affected by the in vivo treatment. MSC from untreated and Imatinib-treated patients displayed normal functional properties (i.e. proliferation, immunophenotype, differentiation and hematopoietic supportive capacity) - but a decreased frequency. In vitro, Imatinib lost its effect when discontinued; which suggest that it has a reversible effect on MSC. Therefore it might lose its effect on MSC after discontinuation in vivo. Copyright © 2014 Elsevier Ltd. All rights reserved.