We present a case of axillary hematoma complicating an ultrasound-guided infraclavicular block in a patient with undiagnosed mycotic aneurysms of the peripheral arteries. Mycotic aneurysm is a rare medical condition with well-identified risk factors. When performing regional anesthesia in patients with these risk factors, clinicians should have a high degree of suspicion about the possible existence of vascular anomalies. A preprocedure Doppler study of the block area and real-time guidance of the needle using ultrasound may be useful.