Vascular anomalies of major venous vessels are rarely seen. Moreover, congenital absence of internal jugular vein is extremely uncommon. In our case, a female patient presented with primary unknown left cervical mass. Cervical ultrasonography demonstrated absence of right internal jugular vein. In addition, computed tomography and dynamic magnetic resonance imaging scans confirmed this diagnosis. Compensatory left internal jugular vein enlargement mimicked sort of cervical mass. Venous magnetic resonance imaging images revealed the absence of right internal jugular vein with compensatory left internal jugular vein dominance. In the literature, the agenesis of IJV was mentioned in a case with concomitant multiple problems. Here, an asymptomatic case is reported with an incident diagnosis. No interventions were planned upon the patient's request. It should be kept in mind that any kind of anomalies can be seen during venous access and neck surgery.