Tandem autotransplants are used to treat advanced testis cancer patients but their value compared to a single autotransplant is unknown. To evaluate the results of autotransplant in relapsed testicular/germ cell cancer, data from 300 patients undergoing autotransplants 1989-2002 were reported to the Center for International Blood and Marrow Transplant Research. We compared results for those patients intended to undergo tandem autotransplant procedures (N = 102) versus patients in whom a second autotransplant was not planned (N = 198). Five-year survival probability was 35% (95% confidence interval = 25%-46%) in the planned tandem transplant cohort compared to 42% (35%-49%) in the group not planned to have a second transplant (P = .29). Probability of progression-free survival at 5 years for these cohorts was 34% (25%-44%) and 38% (31%-45%), respectively (P = .50). The planned tandem autotransplant cohort had significantly more advanced disease at diagnosis and greater likelihood of cisplatin resistance. Patients intended to receive tandem transplants had a lower treatment-related mortality at 1 year (3% versus 10%, P = .02). Using propensity score analysis the planned tandem autotransplant cohort had significantly lower treatment-related mortality (P = .044) but no different risk of relapse (P = .541) compared to the planned single transplant cohort. Tandem autotransplants for testicular cancer are associated with less treatment-related mortality than a planned single transplant, with no differences in disease-related outcomes or overall survival at 3 years. Patient selection bias for either transplant approach, however, may affect the results of this observational study; a randomized trial is needed to determine which approach, if either, is better.