One day after a minor accident, an 85-year-old man developed headache and proximal left leg weakness. He was on warfarin due to atrial fibrillation. On hospital admission, a right posterior parasagittal subdural haematoma that was visualised on CT was considered as cause of all symptoms. Although no surgical intervention was performed he stayed for 2 weeks in a neurosurgical ward. Clinical deterioration occurred within the first days as he was not able to stand on his left leg or rise up from the sitting position. Headache had ceased, but the patient reported low abdominal pain. This condition remained stable for over 2 months although haematoma size decreased significantly. He was then examined for the first time by a neurologist who documented typical clinical features of femoral nerve palsy. Pelvic CT established the diagnosis of traumatic iliacus- and iliopsoas-muscle haematoma under anticoagulants as cause of subacute femoral mononeuropathy.