Spontaneous hematoma of the iliopsoas is a rare pathological circumstance; in the majority of cases published in the literature, it is associated with disorders of hemostasis due to anticoagulant treatment or coagulopathies. We present a case of a 64-year-old man on acenocoumarol, an anticoagulant of the vitamin K antagonist family, for atrial fibrillation, who presented with a severe left hip and flank pain with a huge ecchymosis on the left flank and a partial inability to extend the left thigh. A CT scan confirmed the diagnosis of iliopsoas hematoma. Given the hemodynamic stability of the patient, he benefited from a conservative treatment with a favourable evolution. This case highlights the underlying conditions, diagnosis, and treatment of this uncommon complication.