Iliopsoas hematoma is an uncommon clinical entity that may develop in association with anticoagulation states, coagulopathies and hemodialysis, or anticoagulant therapy. Here, we report a case of unilateral iliopsoas hematoma in a 60-year-old man who received low-molecular-weight heparin for anticoagulation due to continuous veno-venous hemofiltration. The patient presented with fever and productive cough for 2 days. He received continuous veno-venous hemofiltration due to rising blood urea nitrogen (22.7 mmol/L; normal references: 3.2-7.1 mmol) and creatinine (1345 µmol/L; normal references: 53-106 µmol/L). Low-molecular-weight heparin (enoxaparin, 3500-5500 Da, 5-10 IU/kg/h) was delivered continuously by pumps for anticoagulation therapy. At day 12 post heparin treatment, the patient complained left back pain. Platelet count (243 × 109/L) was normal, but both activated partial thromboplastin time (67.5 s) and prothrombin time (17.3 s) were prolonged. Abdominal computed tomography scan revealed left iliopsoas swelling with an indistinct border. Low-molecular-weight heparin was discontinued. Anti-Xa was not monitored throughout the treatment. No improvement was seen, and 3 days later, the patient died after his family decided to terminate therapy. This case highlights the needs for careful anticoagulation as well as close monitoring, and particularly the use of anti-Xa to guide the treatment.