We present a case of a lumbar pseudoaneurysm in a 62-year-old patient with myelofibrosis (agnogenic myeloid metaplasia). The patient was submitted to two anesthetic infiltrations for lumbar pain and one biopsy of a suspected hematopoietic site. Subsequently, a 4.5 cm lumbar pseudoaneurysm was diagnosed. The pseudoaneurysm was thrombosed with 1 ml (500 IU) thrombin injection with a successful clinical result. We discuss different treatment options along with several issues related to the most frequent complication of this technique, namely, native artery thrombosis.