RATIONALE: Few reports in the literature describe internal jugular vein fenestration or duplication, and these are typically incidental surgical findings, which include a few 3-dimensional radiological images of these anomalies obtained from preoperative imaging. The potential of ultrasound has been greatly underestimated because there is no previous literature on ultrasound-based diagnosis of this disease. PATIENT CONCERNS: A 40-year-old woman presented with dizziness. A computed tomography arteriography examination of the head and neck at another hospital found no abnormalities. The magnetic resonance imaging of the head also showed no abnormalities, and the echocardiogram was normal. Psychological tests revealed no significant anxiety. DIAGNOSES: Vascular ultrasound revealed duplication/fenestration of the internal jugular vein, and jugular venography ultimately confirmed this vascular malformation. As a result, she was diagnosed with internal jugular vein duplication/fenestration. INTERVENTIONS: Considering the current symptoms did not affect her quality of life, and this vein malformation did not significantly increase the risk of other diseases, she was placed on a clinical observation regimen. OUTCOMES: Her symptoms did not worsen. After 2 years of follow-up, there had been no change in her jugular vascular malformations. LESSONS: Understanding internal jugular vein duplication and fenestration is crucial for clinicians, particularly those involved in head and neck therapy, as these anomalies can significantly affect surgical outcomes and patient safety. Preoperative imaging techniques, such as ultrasound, can aid in identifying these variations, allowing for improved surgical planning and risk management.