Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by chronic, complement-mediated hemolysis, frequently leading to debilitating clinical symptoms and life-threatening complications such as thromboembolism (TE). A retrospective analysis was performed on 301 patients from the South Korean National PNH Registry to describe disease burden and identify TE-associated risk factors. TE was identified in 18 % of patients and was associated with increased risk for mortality [odds ratio (OR), 6.85; P < 0.001]. A multivariate analysis showed that PNH patients with elevated hemolysis [lactate dehydrogenase (LDH) levels ≥1.5 times the upper limit of normal (ULN)] at diagnosis were at significantly higher risk for TE than patients with LDH <1.5 × ULN (OR 7.0; P = 0.013). The combination of LDH ≥1.5 × ULN with the clinical symptoms of abdominal pain, chest pain, dyspnea, or hemoglobinuria was associated with a greater increased risk for TE than elevated hemolysis or clinical symptoms alone. Continuous monitoring of these risk factors is critical for identifying PNH patients at risk for morbidities and mortality and allowing early intervention. (clinicaltrials.gov identifier: NCT01224483).