Purpose: In spite of their osteoconductive potential, the biomaterials used as substitutes for an autologous graft do not show osteoinductive or osteogenic potential. This study evaluated the association of adult mesenchymal stem cells derived from adipose tissue with xenogenic bone graft in bone regeneration in rabbit calvaria. Materials and Methods: Mesenchymal stem cells were harvested from adipose tissue from 12 animals. These cells, combined with hydroxyapatite, were implanted in 12-mm bilateral bone defects created in the calvaria of six rabbits (test group [TG]), whereas only hydroxyapatite was implanted in the defects created in another group of six animals (control group [CG]). One grafted side of each animal was covered by a collagen membrane. After 8 weeks, the animals were sacrificed, and the region of the bone defects was removed and evaluated using histomorphometry and immunohistochemistry. Results: The TG showed higher amounts (P .05) of vital mineralized tissue and nonvital mineralized tissue, 28.24% ± 6.17% and 27.79% ± 2.72%, respectively, compared with the CG, 13.06% ± 5.24% and 13.52% ± 3.00%, respectively. In TG, no difference was observed (P > .05) in the amount of mineralized tissue between the side that was covered by the membrane vs the side without membrane coverage. On the other hand, a statistically significant difference (P .05) was observed in the CG with regard to the amount of mineralized tissue between the sides with and without membrane coverage. Conclusion: These observations suggest that the association of mesenchymal stem cells derived from adipose tissue with a xenogenic bone graft was capable of promoting better bone regeneration compared with the use of a xenograft alone. Use of a membrane did not produce an increase in the regenerative potential for the TG, in contrast to the CG. Keywords: bone healing, bone marrow, cell transplantation, osteogenesis, stem cells