Background: Data on the safety and efficacy of external beam radiation (EBRT) after Yttrium-90 (Y-90) radioembolization for hepatocellular carcinoma (HCC) is limited. We report our experience using EBRT to treat HCC patients who were previously treated with Y-90. Methods: We analyzed 31 HCC patients who received EBRT following Y-90 treatment. Eighteen were treated with photon therapy (40-50 Gy in 5 fractions), and thirteen with proton therapy (42-67.5 Gy in 15 fractions). Twenty-four patients underwent Y-90 segmentectomies, while seven received Y-90 lobar treatment. The median administered Y-90 activity was 44.4 mCi (range 8.3-114.4). Results: Patients had received 1 (n=14), 2 (n=7), or ≥3 (n=10) prior Y-90 treatments. EBRT was administered for various reasons: poor Y-90 response in two patients, technical limitations in 25 patients, and other reasons in four patients. Ten patients had previously received Y-90 within the EBRT area, thirteen outside the EBRT area, and eight in both regions. The median tumor size was 3.8 cm (range 1.6-19.4). Twenty-seven patients had Child-Pugh (CP)-A score, three had CP-B, and one had CP-C baseline liver function. With a median follow-up of 21 months, the 2-year progression-free survival, and overall survival rates were 28%, and 43%, respectively. The 2-year cumulative incidence of local failure was 7%. CP+2 progression was observed in five patients (16%): three had Y-90 delivered outside the EBRT area and two within the EBRT area. Three patients had possible RILD-related deaths. Grade 3+ biliary complications occurred in three patients (10%): one biloma, one liver abscess, and one biliary stricture which resulted in a possible treatment-related death. All three patients had received at least two prior Y-90 treatment overlapping with the area treated with EBRT and had tumors located near the porta hepatis. Conclusions: EBRT for HCC patients previously treated with Y-90 is feasible and offers excellent local control. Hepatic function and biliary toxicities are potential complications and should be weighed against the clinical benefits.