It has been demonstrated that graft survival rates of offspring-tomother and husband-to-wife renal transplants are equivalent to those of other living donors. Although the vast majority of these transplants proceed without incident, we have encountered several instances of hyperacute rejections that are not predicted by a positive cross-match. From 1375 renal transplants performed at our center between 1989- 2005 twelve corresponded to offspring-to-mother (G1) and nine corresponded to husband to wife transplants (G2). All the recipients were multiparous (2 to 5 children). We compare these patients (pts) with other muliparous women (150 pts) who received their graft from living unrelated donors (G3). Pretransplantation lymphocytotoxic cross-match testing were performed by complement dependent citotoxicity with antihuman globulin added (AHG-CDC), being negative in all cases. All the patients received triple-drug immunosuppressive therapy consisted of cyclosporine, prednisolone and mycophenolate mofetil or Azathiopurine. Two pts in G1 (16.6%), two pts in G2 (22.2%) and non in G3 developed hyperacute rejection which led to graft loss. One, three and five year pts and graft survival were not different between remaining pts (Kaplan- meier). (Table 1 and 2) Why under similar conditions some husband to wife and offspring-to-mother kidney transplant recipients developed adverse hum immunological events while others maintain excellent longterm graft outcome? It is possible to speculate that for some women pregnancy is in fact a sensitizing event, while in others it promotes 'tolerance'