Prevascularization of engineered bony constructs can potentially improve in vivo viability. However, the effect of endothelial cells on osteogenesis is unknown when placed in poly(D,L-lactide) (PLA) scaffolds alone. Adipose-derived stem cells (ASCs) have the ability to differentiate into both osteoblasts and endothelial cells by culture in specific media. We hypothesized that ASC-derived endothelial cells would improve vascularity with minimal contribution to bone formation when placed in scaffold alone. ASCs were successfully differentiated into endothelial cells (ASC-Endo) and osteoblasts (ASC-Osteo) using media supplemented with vascular endothelial growth factor and bone morphogenic protein 2, respectively. Tissue-engineered constructs were created with PLA matrices containing no cells (control), undifferentiated ASCs (ASCs), osteogenic-differentiated ASCs (ASC-Osteo), or endothelial differentiated ASCs (ASC-Endo), and these constructs were evaluated in critical-size Lewis rat calvarial defect model (n = 34). Eight weeks after implantation, the bone volume and microvessel population of bony constructs were evaluated by micro-computed tomography analysis and histologic staining. Bone volumes for ASCs and ASC-Osteo constructs, 0.7 and 0.91 mm(3), respectively, were statistically greater than that for ASC-Endo, 0.28 mm(3) (P < 0.05). There was no statistical difference between the PLA control (0.5 mm(3)) and ASC-Endo (0.28 mm(3)) constructs in bone formation. The percent area of microvessels within constructs was highest in the ASC-Endo group, although it did not reach statistical significance (0.065). Prevascularization of PLA scaffold with ASC-Endo cells will not increase bone formation by itself but may be used as a cell source for improving vascularization and potentially improving existing osteoblast function.