Background and objective: Stimulating the vagus nerve reduces pain. The purpose of this study was to evaluate the effect of a Valsalva. manoeuvre, which stimulates the vagus nerve, on perception of pain during peripheral venous cannulation in adult patients. Methods: This was a prospective randomized clinical trial. One hundred and ten patients scheduled for elective surgery were randomly divided into two groups. Half of the patients, Group A, underwent venepuncture during a Valsalva manoeuvre and the other half of the patients, Group B, underwent venepuncture without performing a Valsalva manoeuvre. Patients made a pain assessment using a 0-10 point numerical rating scale. Results: The numerical rating scale score was 1.5 +/- 1.2 for Group A and 3.1 +/- 1.9 for Group B, the difference being statistically significant (P < 0.0001). Conclusions: On the basis of data from this study, the Valsalva manoeuvre may be of the value before venous cannulation as a simple and practical method to reduce pain from venous cannulation.