Paracrine interactions between adipocytes and microvascular endothelial cells may play a key role in the regulation of adipose tissue growth. In this paper, we describe new 2D and 3D adipocyte-endothelial cell co-culture models and their growth and differentiation characteristics. To establish these models, we have first developed a defined medium that is suitable for the co-culture of 3T3-L1 adipocytes with human umbilical vein endothelial cells (HUVEC). Interestingly, HUVEC viability and growth is significantly enhanced in the developed co-culture medium in the presence of the adipocytes, whereas they are moderately decreased (compared to commercially available standard HUVEC media) in the absence of the adipocytes. Experiments in both 2D, direct contact co-culture and 3D, collagen co-culture using EGFP-labeled preadipocytes showed that HUVEC promote (3T3-L1) preadipocyte proliferation. The growth ehancement effect is proportional to the initial seeding ratio of HUVEC to 3T3-L1 cells. For example, with an initial seeding ratio of 3 to 1, the co-culture increased the proliferation of 3T3-L1 cells by ca. 3-fold compared to 3T3-L1 cells-only control cultures. In the 3D co-culture, we have also observed a vascular network formed by differentiated HUVEC. Taken together, the results to date suggest that the 3T3-L1-HUVEC co-cultures afford improved growth and differentiation of both the adipocyte and endothelial cell components. Prospectively, these types of models should facilitate controlled, yet physiologically relevant studies on direct and paracrine interactions between preadipocytes, adipocytes and endothelial cells in adipose tissue development.