Although the global vascular guidelines recently proposed the Global Limb Anatomic Staging System (GLASS) as an anatomical classification for chronic limb-threatening ischaemia (CLTI), prediction of perioperative outcomes using the GLASS classification in patients with CLTI due to isolated below-the-knee (BTK) lesions has not been well studied.This retrospective study included 585 patients with CLTI due to isolated BTK lesions who underwent endovascular therapy (EVT). The severity of arterial lesions was graded using the GLASS infrapopliteal (IP) and inframalleolar (IM) classifications and defined as follows: non-severe IP, 0–3; severe IP, 4; non-severe IM, P0–1; and severe IM, P2. The outcome measures were technical failure, defined as recanalisation failure of the target artery path, and perioperative failure, defined as a composite of all-cause death, major amputation, or repeat revascularisation within 30 days.Technical and perioperative failures occurred in 9.4% (n = 55) and 9.9% (n = 58) patients, respectively. Compared to patients with non-severe IP and IM, those with both severe IP and IM were significantly associated with technical and perioperative failures (odds ratio [OR]: 13.87 [95% confidence interval (CI) 4.69–41.02, P < 0.001] and OR: 2.18 [95% CI 1.08–4.38, P = 0.041], respectively).The GLASS classification may have predictive value for technical and perioperative failure in patients with CLTI due to isolated BTK lesions after EVT.