Prediction of the final transferred fat volume is essential for the success of fat grafting, but remains elusive. Between 20 and 80 % of the initial transplanted volume can be creabsorbed. Although graft survival has many determinants, CD34+ progenitor cells from the vascular stroma of adipose tissue play a central role by promoting growth of blood vessels and adipocytes. We aimed to verify the hypothesis that a higher proportion of total CD34+ cells in the transplant is associated with better preservation of the graft volume. Human lipoaspirates from 16 patients were processed by centrifugation and two grafts per donor were subcutaneously injected into 32 nude mice in 1 ml volumes in the right upper flank area. The volume of each graft was measured using a preclinical MRI scanner immediately after grafting and at three months. The percentage of CD34+ cells in the graft before implantation was determined by flow cytometry. The final graft volume at three months after implantation directly correlated with the percentage of CD34+ cells in the grafted material (r = 0.637, P = 0.019). The minimum retention of the fat graft was 28 % and the maximum retention was 81 %, with an average of 54 %. Our study found that fat retention after fat transfer directly correlated with the fraction of CD34+ cells in the graft. The simple and fast determination of the CD34+ cell percentage on site can help predicting outcomes of fat transplantation. and Corresponding authors: Ondřej Měšťák, Luděk Šefc