BACKGROUND: Bilateral stent-in-stent(SIS) self-expandable metal stent placement is technically challenging for palliation of unresectable malignant hilar obstruction. In the SIS technique, the uniform large cell type biliary stent facilitates contralateral stent deployment through the mesh of the first metallic stent. This study aimed to assess the technical success and clinical effectiveness of this technique with a uniform large cell type biliary stent.METHODS: Thirty-one patients who underwent bilateral SIS placement using a large cell type stent were reviewed retrospectively. All patients showed malignant hilar obstruction(Bismuth types Ⅱ,Ⅲ,Ⅳ) with different etiologies.RESULTS: Sixteen(51.6%) patients were male. The mean age of the patients was 67.0±14.0 years. Most patients were diagnosed as having hilar cholangiocarcinoma(58.1%) and gallbladder cancer(29.0%). Technical success rate was 83.9%.Success was achieved more frequently in patients without masses obstructing the biliary confluence(MOC) than those with MOC(95.2% vs 60.0%, P=0.03). Functional success rate was 77.4%. Complications occurred in 29.0% of the patients. These tended to occur more frequently in patients with MOC(50.0% vs 19.0%, P=0.11). Median time to recurrent biliary obstruction was 188 days and median survival was 175 days.CONCLUSIONS: The large cell type stent can be used efficiently for bilateral SIS placement in malignant hilar obstruction. However, the risk of technical failure increases in patients with MOC, and caution is needed to prevent complications for these patients. BACKGROUND: Bilateral stent-in-stent (SIS) self-expandable metal stent placement is technically challenging for palliation of unresectable malignant hilar obstruction. In the SIS technique, the uniform large cell type biliary stent facilitates contralateral stent deployment the mesh of the first metallic stent. This study aimed to assess the technical success and clinical effectiveness of this technique with a uniform large cell type biliary stent. METHODS: Thirty-one patients who underwent bilateral SIS placement using a large cell type stent were reviewed retrospectively. Sixteen (51.6%) patients were male. The mean age of the patients was 67.0 ± 14.0 years. Most patients were diagnosed as having hilar cholangiocarcinoma (58.1% ) and gallbladder cancer (29.0%). Technical success rate was 83.9%. Success was achieved more frequently in patients without masses obstructing the bi Functional success rate was 77.4%. Complications occurred in 29.0% of the patients. These tended to occur more frequently in patients with MOC (50.0% vs 60.0%, P = 0.03) vs 19.0%, P = 0.11). Median time to recurrent biliary obstruction was 188 days and median survival was 175 days. CONCLUSIONS: The large cell type stent can be used efficiently for bilateral SIS placement in malignant hilar obstruction. However, the risk of technical failure increases in patients with MOC, and caution is needed to prevent complications for these patients.