Adult mesenchymal stromal cells (MSC), also referred to as mesenchymal stem cells, were detected almost half a century ago in bone marrow and have been studied intensively in the last decade. Different aspects of MSC biology were explored and published. Studies pointed to their localization in different organs during development and in adulthood and described their characteristics in experimental or clinical investigations. Despite intensive research in the field and in sharp contrast to hematopoietic stem cells (HSC), it has become more and more clear that MSC lack a unique cell surface marker. MSC not only share cell surface markers with other types of cells, they also share many features with pericytes and fibroblasts, including their capability to differentiate into, for instance, osteoblasts or adipocytes. In this review we therefore screen the current literature to disclose differences between MSC and fibroblasts and also report on common qualities.