In patients treated with allogeneic stem cell transplantation (SCT) for malignant disease who suffer from a relapse after the transplantation, the role of second allogeneic SCT is often uncertain. In a retrospective analysis, 2632 second allogeneic transplantations carried out for a relapse after the first transplantation were analyzed to define indications and identify predictive factors. Fifteen percent of the patients remained relapse-free until 5 years after the second SCT. Patients with CML had a better survival than patients with other diseases. In a multivariate analysis, factors associated with better survival were low disease burden, longer remission duration after the first transplantation, longer interval between the transplantations, younger age, absence of grade II-IV acute GvHD or chronic GvHD after the first transplantation, and later year of transplantation. The European Society for Blood and Marrow Transplantation risk score predicted the outcome. Using the same donor as in the first transplantation vs another donor had no predictive value for survival. Sibling donor was a favorable predictive factor. In conclusion, second allogeneic SCT offers a reasonable option especially for young patients with a long remission after the first transplantation and a low disease burden. The present findings do not support the usefulness of changing the donor for the second transplantation.