Spontaneous iliopsoas muscle haematoma is a rare complication in patients receiving anticoagulants. We present the case of spontaneous iliopsoas muscle haematoma in a 68-year-old male patient under anticoagulant therapy with dicumarol in combination with acetylsalicylic acid 100 mg. The patient was admitted with clinical symptoms of sudden pain and extensive swelling along his left abdominal lower quadrant, and clinical findings of a hard, pulseless, painful swelling of the left lateral abdomen with pain extending along the left femoroinguinal region. His pulse rate was 92/min and blood pressure 120/85 mm Hg. Laboratory investigations indicated a grossly deranged INR (17.7) and a drop in Hct (22.0%). The diagnosis of a left iliopsoas muscle haematoma was established with ultrasonography and computed tomography. The patient was managed conservatively with administration of fluids and a blood transfusion while the coagulation profile was corrected with vitamin K and fresh frozen plasma. The spontaneous iliopsoas muscle haematoma in patients who are on anticoagulant treatment is uncommon and its management controversial since approaches to therapy vary among conservative, interventional radiology and open surgery, depending on the cause and volume of the haematoma, timing of diagnosis, degree of neurological impairment and haemodynamical stability.