RESUMO
Femoral vein duplication is an anatomical abnormality with high prevalence in general population. Its diagnosis is through imaging exams, with greater emphasis on Doppler ultrasonography. The identification is crucial because it masks the clinical symptoms of deep vein thrombosis. Besides being an important anatomical pathway and, while in duplicity, it can be used as a possible vascular substitute, therefore making the knowledge of the anatomical path and its variants essential. Ultrasonography has attractive advantages over other methods, collecting data from patients in physiological conditions with- out the need of contrast, or exposure to ionizing radiation, providing anatomical details of the venous system and anatomical variations. When thrombus is suspected in a duplicated segment, examination of the lower limb with anatomical variation should not be used to justify the presence of duplication in the contralateral limb.