Purpose <p>To evaluate the prognostic value of the aspartate aminotransferase-to-platelet ratio index (APRI) for overall survival (OS) after transarterial radioembolization (TARE) in patients with intrahepatic cholangiocarcinoma (ICC) and hepatocellular carcinoma (HCC) from the prospective study CIRT (CIRSE study on SIR-Spheres Therapy).</p> Materials and Methods <p>Adult patients treated with TARE Y-90 were included. Baseline, laboratory, treatment, and follow-up data were collected prospectively. Receiver operating characteristic analysis was used to determine optimal APRI cut-offs. OS from the date of TARE was analysed using Kaplan–Meier. Propensity score matching and multivariable Cox regression analyses were performed.</p> Results <p>103 ICC and 377 HCC patients were analysed. Most patients had ECOG 0 (58.3%/61.3%) or 1 (31.1%/31.8%) in the ICC and HCC groups, respectively. Median APRI was 0.5 (IQR: 0.3–0.8) in ICC and 0.8 (IQR: 0.4–1.4) in HCC. Higher APRI values were associated with significantly shorter OS in both cohorts using different thresholds (ICC: APRI &gt; 0.4; HCC: APRI &gt; 0.7). These associations remained significant after propensity score matching and multivariable analysis. APRI was an independent prognostic factor for OS in both ICC (95% CI 1.25–5.23; <i>p</i> = 0.010) and HCC (95% CI 1.04–2.06; <i>p</i> = 0.028). The identified APRI cut-offs were associated with survival differences when body surface area (BSA) and modified BSA dosimetry were used, but not with partition model dosimetry.</p> Conclusion <p>APRI may be a promising, easily accessible prognostic biomarker for OS after TARE in ICC and HCC patients. Its prognostic value may be influenced by tumour type and counteracted by dosimetry method, supporting further investigation on this topic.</p> <p><i>Trial registration</i> NCT02305459 </p> Graphical Abstract