Adipose tissue includes various cell types beyond the typical adipocytes. The stromal vascular fraction (SVF) contains mesenchymal stem cells (MSCs), pericytes, and endothelial cells, which can be isolated from adipose tissue by mechanical and enzymatic methods. The composition of the SVF is heterogeneous, and donor factors such as sex, age, body mass index (BMI), and harvesting site are associated with variations in cellular composition and viability. The expression of specific surface markers, which determine the immunophenotype of the cells, can also vary. In this study, we investigated the effects of donor age, BMI, and harvesting site on cell yield, viability, and size. Our results showed that BMI significantly influenced cell yield and size, with overweight and obese donors yielding more cells than normal-weight donors. Additionally, cells isolated from the adipose tissue of the thighs/legs were larger than those from other areas. Flow cytometry showed considerable variability in SVF composition among donors. These results emphasize that SVF donor characteristics have a significant impact on cell yield, viability, and cell size, with the immunophenotype being highly donor-dependent. Understanding these factors is crucial for optimizing cell yield and defining populations for therapeutic applications of SVF cells.