BACKGROUND: The external jugular vein (EJV) is a useful intravenous (IV) cannulation site for anesthesiologists, although it has a relatively high failure rate. Unlike other central veins, visualization of the EJV is important during IV cannulation, and the Valsalva maneuver distends the jugular venous system. However, the relationship between the maneuver and EJV visibility remains unknown. This study compared EJV visibility before and after the Valsalva maneuver. METHODS: This was a prospective observational study that included 200 participants. After the induction of anesthesia, EJV visibility grade, depth from the skin to the EJV superficial surface (EJV depth), and EJV cross-sectional area (CSA) before the Valsalva maneuver were measured. The same parameters were measured after the Valsalva maneuver was performed. The EJV visibility grade was defined as grade A: good appearance and good palpation, grade B: poor appearance and good palpation, and grade C: poor appearance and poor palpation. RESULTS: Patient body mass index and EJV depth affected the EJV visibility grade before the Valsalva maneuver (p < 0.05), although EJV CSA did not. The Valsalva maneuver distended EJV CSA and reduced EJV depth, although these changes were not correlated with EJV visibility grade. With regard to EJV visibility, 34.0% of grade B cases and 20.0% of grade C cases were improved by the Valsalva maneuver. CONCLUSIONS: Although the Valsalva maneuver improved EJV CSA and EJV depth, it did not greatly affect EJV visibility grade.