Background. Mycotic aneurysms are rare but possibly fatal vascular infection. The incidence of mycotic aneurysms has been gradually rising because of an increase in the risk factors for atherosclerosis and immunosuppression. The source of the infection could be bacterial, viral, or fungal. Objective of the study. Presentation of a rare clinical case of the spontaneous infected mycotic aneurysm of the superficial femoral artery treated by surgical bypass. Material and methods. Clinical and paraclinical data were retrieved from the electronic case record. The literature about similar cases has been studied. Results. A 61-years-old female was admitted with pain in the thigh, restriction of knee extension, malaise, and fever. Disease started 2 months before with unexplained fever. Later, patient began to have some knee pain interpreted as an arthritis. One week before admission, she observed presence of a painful thigh mass that gradually enlarged. At admission, the pulsatile mass with systolic bruit was noted in the lower thigh. CT angiography showed 7 cm aneurysm of the superficial femoral artery with a fluid around the sac. Aneurysm was resected and autogenous femoral to distal popliteal bypass was constructed. Cultures were negative. Patient was discharged with palpable pedal pulses and followed for 2 years with no relapse of infection. Conclusion. In a patient with unexplained fever and limb pain the mycotic aneurysm should be considered in a differential diagnosis. Emergency surgical treatment represent a unique treatment approach.