Abstract Introduction The transplantation of genetically modified progenitor cells such as bone marrow-derived mesenchymal stem cells (MSCs) is an attractive strategy to improve the natural healing of articular cartilage defects. In the present study, we examined the potential benefits of sustained overexpression of the mitogenic and pro-anabolic insulin-like growth factor I (IGF-I) via gene transfer upon the biological activities of human MSCs (hMSCs). Methods Recombinant adeno-associated vectors (rAAV) were used to deliver a human IGF-I coding sequence in undifferentiated and chondrogenically-induced primary hMSCs in order to determine the efficacy and duration of transgene expression and the subsequent effects of the genetic modification upon the chondrogenic versus osteogenic differentiation profiles of the cells relative to control ( lacZ ) treatment after 21 days in vitro . Results Significant and prolonged expression of IGF-I was evidenced in undifferentiated and most importantly in chondrogenically-induced hMSCs transduced with the candidate rAAV-hIGF-I vector for up to 21 days, leading to enhanced proliferative, biosynthetic, and chondrogenic activities compared with rAAV- lacZ treatment. Overexpression of IGF-I as achieved in the conditions applied here also increased the expression of hypertrophic and osteogenic markers in the treated cells. Conclusions These results suggest that a tight regulation of rAAV expression may be necessary for further translation of the approach in clinically relevant animal models in vivo . However, the current findings support the concept of using this type of vector as an effective tool to treat articular cartilage defects via gene- and stem cell-based procedures.