Purpose: This study analyzed the use of bone marrow-derived mesenchymal stem cells and adipose tissue-derived stem cells, associated with xenograft, in appositional reconstructions in rabbit calvaria using histomorphometry. Materials and Methods: Fifteen New Zealand rabbits, weighing 3.5 to 4.0 kg and aged between 10 and 12 months, were randomly divided into three groups. Appositional bone reconstruction situations were created in the calvaria of the animals using titanium cylinders, fitted with titanium occlusive caps. Bone decortication was performed to promote bleeding. Inside the cylinders, only xenograft was positioned in the control group (CG; n = 5); xenograft combined with mesenchymal bone marrow-derived stem cells was positioned in group 1 (G1; n = 5), and a xenograft combined with adult mesenchymal stem cells derived from adipose tissue was positioned in group 2 (G2; n = 5). After 56 days, all rabbits were euthanized and their parietal bones processed for histomorphometric analysis, and the following parameters were evaluated: newly formed bone; residual graft particles; soft tissue; vital bone titanium contact, also called the level of osseointegration; and the level of bone volume contained inside the cylinders, also called the internal bone volume. Results: The histomorphometric study revealed the following for CG, G1, and G2: newly formed bone of 18.96% ± 9.00%, 27.88% ± 9.98%, and 22.32% ± 7.45%; residual graft particles of 28.43% ± 2.44%, 23.31% ± 3.11%, and 27.58% ± 3.98%; soft tissue of 52.61% ± 10.80%, 50.23% ± 8.72%, and 49.90% ± 8.76%; vital bone titanium contact of 4.98% ± 4.30%, 34.91% ± 7.82%, and 20.87% ± 5.43%; and internal bone volume of 88.36% ± 25.97%, 98.73% ± 19.05%, and 98.52% ± 19.87%, respectively. No statistical difference between groups for newly formed bone, residual graft particles, soft tissue, and internal bone volume (P > .05) were verified. Conclusion: Regarding vital bone titanium contact, it was observed that the use of bone marrow mesenchymal stem cells, when compared with the adipose mesenchymal stem cells, showed the highest level of osseointegration, and both of them obtained superior levels to the xenograft alone. Keywords: adipose tissue-derived mesenchymal stem cells, bone marrow-derived mesenchymal stem cells, bone regeneration, cell transplantation