Background: Retroperitoneal radiation therapy or systemic chemotherapy with 3 cycles PEB represent the guideline recommended treatment options in marker negative clinical stage IIA/B seminoma. Despite a high cure rate of 90% to 94% and 82% to 90% in CS IIA and IIB, respectively, both therapeutic options are associated with significant long-term toxicities. It was the aim of our trial to evaluate the feasibility, oncological efficacy and treatment associated morbidity of primary nsRPLND in stage IIA/B seminoma. Methods: 16 patients with marker negative clinical stage IIA and IIB classical seminoma of the testis were recruited in the prospective trial. Patients with primary metastatic stages IIA/B or patients who developed metastatic during active surveillance for clinical stage I seminoma could be recruited. Metastatic disease following carboplatin therapy for clinical stage I seminoma represented an exclusion criteria. Informed consent was obtained after educational talk about the standard treatment options. Surgery associated complications were classified according to Clavien-Dindo. Progression-free survival and overall survival were calculated by Kaplan-Meier curves. Results: Mean age was 37.2 (21-54) years. Mean follow-up is 21.2 (1-36) months. All patients were treatment-naïve and 9 (56.2%) and 7 (43.8%) patients were diagnosed with stage IIA/B at time of primary diagnosis or during active surveillance for clinical stage I disease, respectively. 13 (81.2%) and 3 (18.8%) patients were diagnosed with stage IIA and IIB disease, respectively. 14 (87.5%) and 2 (12.5%) patients underwent open and robot assisted ns RPLND, respectively. Mean OR time was 131 (105-195) min, mean blood loss was < 150ml and the mean hospitalization time was 4.5 (3-9) days. We did not observe surgery associated complications > Clavien Dindo grade 3a. 14/16 (87.5%) patients preserved antegrade ejaculation. Histology of the resected lymph nodes revealed metastatic seminoma in 12 (75%) patients; 1 and 3 patients demonstrated embryonal carcinoma and inflammatory disease, respectively. 2/16 (12.5%) patients developed an outfield relapse 4 and 6 months postoperatively. Both patients were salvaged by systemic chemotherapy with 4 cycles PEB. Conclusions: NsRPLND results in a high cure rate at midterm follow-up and it is associated with a low frequency of treatment associated morbidities making this approach a feasible alternative to standard radiation therapy or systemic chemotherapy. Clinical trial information: DRKS00025384.