Background: Single-center observational studies have established the use of single or tandem SCT to salvage relapsed GCT but randomized trials are lacking. We analyzed outcomes and prognostic factors in 2,395 male SCT recipients for relapsed GCT between 1990 and 2015. Methods: Recipients of single or tandem SCT reported to the Center for International Blood and Marrow Transplant Research were identified. Outcomes were compared by SCT year: 1990-94 (N = 288), 1995-99 (N = 351), 2000-04 (N = 376), 2005-09 (N = 509) and 2010-15 (N = 871). A recent subset (n = 267, 2000-2015) with detailed disease- and transplant-related data was further analyzed with a multivariate (MVA) Cox proportional hazards model. Results: Median age at SCT was 31 (11-76) years and 49% received SCT within 12 months of diagnosis consistent with early relapse/primary refractory GCT. 26% had primary extragonadal GCT; 1,167 (49%) had intent to tandem transplant (TT). The median follow up was 51 (3-313) months. Day 100 non-relapse mortality was statistically similar at 8% in 1990-94 (vs. 4% in 2010-15) but 3-year progression-free survival (PFS) improved from 24 (18-31)% in 1990-94 to 47 (43-50)% in 2010-15 (p < 0.0001) and 3-year survival (OS) from 35 (29-40)% to 54 (50-57)% in 2010-15 (p < 0.0001). Compared with single SCT, TT recipients were younger 31 (16-62) vs 34 (13-76), with lower Hematopoietic Cell Transplantation-Comorbidity Index, more likely to undergo SCT after 1 line of chemotherapy (28% vs 9%), and within 1 year of diagnosis (51% vs 38%). TT was preferred over single SCT over time (48% of SCT were TT in 2000-04 vs. 81% in 2010-15). In MVA, non-seminoma histology, residual tumor at SCT, receipt of > 1 line of pre-SCT chemotherapy and single SCT (vs. TT), were associated with worse PFS and OS. Year of SCT was not significant when adjusted for these covariates. Conclusions: In this large longitudinal cohort, improvements in PFS and OS were observed in recent years. SCT earlier in disease course and tandem SCT were associated with superior outcomes. These data involving a large cohort reported from 225 centers confirm specialized centers’ date in a real-world setting.