This study concerns the cytogenetic stability of in vitro human bone marrow-derived mesenchymal stem cells (MSCs) in primary culture and after passaging. Bone marrow samples were collected from seven brain malfunction patients involved in autologous MSC transplantation trials. Chromosome preparations from primary MSC cultures and after 3 passages were analyzed by conventional staining and G-banding techniques. All MSCs showed normal diploid karyotypes, 46 XY or 46 XX, without aneuploidy or polyploidy; chromosome structural abnormalities were not detected. The results indicate that the in vitro cultured MSCs retained normal cytogenetics before being transplanted back into the patients.