Abstract Background Complication rate in patients with chronic thrombo-embolic pulmonary hypertension (CTEPH) who undergo balloon pulmonary angioplasty (BPA) is high, especially in patients with compromised pulmonary hemodynamics. Purpose Here we describe complications based on the new definition in a cohort of CTEPH patients who underwent BPA. Methods All patients with CTEPH who completed BPA treatments before September 15th 2023 were selected from the CTEPH database. Peri-procedural complications were collected and classified according to the 2023 consensus paper on BPA in CTEPH patients. Complications were analyzed in subgroups of patients with pulmonary vascular resistance (PVR) or >6.6 WU and mean pulmonary artery pressure (mPAP) or >45 mmHg at first BPA. Results In total, 87 patients (63.2% women; mean age 61.1±14.0 years; 62.1% on dual PH targeted medical therapy) underwent 426 (mean 4.9±1.6 per patient) BPAs. Non-severe complications occurred in 59 (13.8%) of the interventions; in 47.1% of the patients; 64.4% were thoracic, and 35.6% were non-thoracic complications. The thoracic complications were mostly mild (71.1%) or moderate (28.9%), and none were severe. Patients with a PVR >6.6 WU (n=8) underwent more BPA-procedures (6.6±1.5 versus 4.6±1.5, p=0.002), had more overall complications (87.5% versus 40.6% of patients, p=0.020), and more thoracic complications (17.0% vs 6.8% of BPAs, p=0.013) than patients with PVR 6.6 WU. Patients with mPAP >45 mmHg (n=13) also had more BPA-procedures (6.5±1.7 versus 4.6±1.4, p<0.001), more overall complications (76.9% versus 43.5% of patients, p=0.027) and more thoracic complications (14.1% versus 7.9% of BPAs, p=0.039) than patients with mPAP 45 mmHg. Conclusions Complications occurred in 13.8% of BPA procedures and were mostly mild. Patients with increased pulmonary hemodynamics at baseline suffered more (thoracic) complications.Overview complications