Background: We thought to evaluate progression-free survival of stage II A/B seminoma patients (pts) undergoing primary retroperitoneal lymph node dissection (RPLND) without adjuvant treatment. Aim is to present interim data of a feasibility study and a phase II trial. Methods: Prior to the phase II study, 9 patients have been treated within a pilot feasibility study. After IRB approval, additional 12 patients from 3/2016 to 9/2018 within the prospective phase II trial were accrued. All patients received primary retroperitoneal lymph node dissection (open or daVinci assisted) for stage IIA/B seminoma without adjuvant treatment. The data was analyzed for peri- and postoperative outcome including recurrence free survival. The trial will have to accrue 30 pts and was designed to exclude a > 30% recurrence to standard treatment. Results: Since 5.2014 twenty-two patients with seminomateous germ cell tumor have been included in both studies, including one patient with an atypical inguinal recurrence and one patient with a 6 cm marker negative recurrence (clinical stage IIC). Primary RPLND was performed in 4 patients with initial CSIIA. 14 and 4 patients experiences a recurrence under surveillance and after carboplatin adjuvant treatment, respectively. Mean tumor size was 2.6 cm with a mean OR time of 134 min and a mean blood loss of 70 cc. One patient after DaVinci RPLND developed a ureteral stricture requiring ileal ureter substitute. The mean follow-up is 24 month (range 1-51 months), 17/22 patients (77%) are free of recurrence. 5/22 (23%) developed a recurrence (4x outside field and 1x inside field) with a mean time to recurrence of 4.5 months. All patients received salvage treatment (4x CTX and 1x radiotherapy) and are currently recurrence free. Conclusions: Primary RPLND in stage IIA/B seminoma patients is an experimental treatment approach in order to reduce long term toxicity and secondary malignancies. Interim results of this strategy justifies continuation of the study. This kind of surgery should only be performed within clinical trials in high volume referral centers. Clinical trial information: NCT 2015053664.