Purpose: To evaluate the feasibility of enrolling patients in a randomized controlled trial (RCT) comparing endovascular coils (EC) and vascular plugs (VP) for proximal splenic artery embolization (pSAE) in high-grade splenic trauma, and to collect data to inform the design of a larger clinical effectiveness trial. Methods: Single-center, prospective, RCT of patients with Grade III–V splenic injuries selected for nonoperative management. Patients were randomized to pSAE with EC or VP. The main outcome was feasibility. We also evaluated technical success, time to stasis, complications, mortality, and splenectomy rates, by estimating rates and 95% confidence intervals. Results: 46 of 50 eligible patients were enrolled (92%, 95% CI 90–100%). Overall, splenic salvage was 98% (45/46; 95% CI 94–100%). Primary technical success was observed in 22 EC patients (96%; 95% CI 87–100%) and 20 VP patients (87%; 95% CI 73–100%). Bayesian analysis suggests a > 80% probability that primary technical success is higher for EC. Two complications (one major and one minor) occurred in the EC group (9%; CI 0–20%) and one major complication occurred in the VP group (4%; CI 0–13%). Conclusions: Randomized comparisons of endovascular devices used for pSAE after trauma are feasible. pSAE using either EC or VP results in excellent rates of splenic salvage in trauma patients with high-grade splenic injuries. These high rates of splenic salvage and low rates of complications make their use as a primary outcome in a future trial problematic. Consideration should be given to technical parameters as a primary outcome for future trials.