Rectus sheath haematoma, an uncommon complication related to subcutaneous administration of enoxaparin, has overall mortality of 4%. Possible mechanisms include unintended intramuscular injection of enoxaparin, and enhanced anticoagulant effect in the elderly and patients with increased bleeding risk. We describe the case of an 80 year-old female patient who was treated after a non-ST-elevated myocardial infarction, with enoxaparin, aspirin and clopidogrel. After a single dose of enoxaparin, the patient developed massive rectus sheath haematoma that was promptly diagnosed and was surgically managed. The patient recovered uneventfully. With incremented use of low-molecular weight heparins in the elderly, one may expect a growing number of bleeding complications.