Background: Surgical resection of post-chemotherapy residual masses for metastatic seminoma is discussed controversially with regard to oncological and functional outcome. Furthermore, the role of FDG-PET/CT to detect vital seminoma is still unclear. It is the aim of this study is to report the outcomes of patients with pure seminoma who underwent PC-RPLND. Methods: In this retrospective multi-institutional study, pure seminoma patients whounderwent PC-RPLND for marker negative, FDG-PET/CT positive residual masses > 3cm or marker negative retroperitoneal relapse following first line chemotherapy between 2000 and 2023 were included. Patients with residual masses and negative FDG-PET/CT, inadequate systemic chemotherapy, insufficient clinical data, positive markers, or with residual or relapsing masses following salvage chemotherapy were excluded. Perioperative and long-term outcomes were reviewed. Results: 109 patients were included. All patients received first-line cisplatin-based chemotherapy. Clinical features of the patients are presented in the table. 92.6% of PC-RPLNDs were performed via an open transperitoneal approach. 61 (55.9%) and 48 (44.1%) pts underwent unilateral and a full bilateral resection, resp. Adjunctive surgery was performed in 46 (42%) pts, the most common of which were ureteral resection/repair in 16 (15%) pts, and vascular resection/repair in 14 (13%) pts. Median (IQR) blood loss and length of hospital stay were 550 (300 – 5800) mL and 4 (2 – 18) days, resp. Clavien - Dindo complications ≥ 3a developed in 11 (10.1%) pts. Final pathology revealed necrosis/fibrosis in 75 (69%) and seminoma in 34 (31%). FDG-PET/CT for residual masses > 3cm showed a positive predictive value of only 20%. Except for marker negative progression (p<0.001), no reliable clinicopathologic parameters were identified to predict presence of viable seminoma. With a median (IQR) follow-up of 56 (2 – 164) months, 15 (14%) patients relapsed (12 with lymph node, 3 with visceral/skeletal metastases). 3 (3%) patients died of disease. Conclusions: One third of patients with progressive or > 3cm FDG-PET-CT positive residual retroperitoneal masses following first-line chemotherapy for metastatic seminoma may have viable tumor. FDG-PET/CT has a poor positive predictive value and might be omitted as staging procedure. In selected cases, PC-RPLND may be a valuable option if performed in high-volume centers with expertise in testicular cancer management.