One strategy of adipose tissue engineering is to transplant adipocytes or adipocyte precursor cells in combination with polymeric materials. However, a satisfying formation of fat tissue and its long-term survival still remain major problems. There is increasing evidence that treatment of the cells prior to implantation plays a critical role in the success of adipose tissue growth. In a previous study, we established a model system based on 3T3-L1 cells that allows for reproducible engineering of mature, coherent adipose tissues in vitro. We utilized this model system in the current study and systematically investigated the long-term in vivo development of cellular constructs with varying stages of adipogenic development at the time point of implantation. Blank polyglycolic acid fiber meshes, scaffolds seeded with uninduced 3T3-L1 preadipocytes, and cell-polymer constructs precultivated under adipogenic conditions for 2, 9, or 35 days were implanted subcutaneously into nude mice. Histological analysis revealed that no fat formation occurred in constructs without adipogenic precultivation. Implantation of mature fat pads (35 days) resulted in adiponecrosis within the constructs. In contrast, implants with an immature phenotype at the time point of implantation (2 and 9 days) gave rise to vascularized, mature adipose tissue in vivo. Further, these engineered adipose tissues showed long-term survival in vivo over the whole investigation period of 24 weeks. The results of this study can contribute to the development of future clinical approaches as they give clear evidence which precultivation strategy promotes successful development and long-term survival of engineered adipose tissue.