A vertical VAS is a valid instrument for monitoring headache pain intensity.

Visual analogue scales (VAS) are well-validated instruments for assessing pain intensity, but have an impractical format. The aim of the study was to validate a vertical against a horizontal VAS for pain intensity registration. Out-patients with headache or non-headache pain were included. Participants completed a horizontal and a vertical VAS. Both were completed twice for test-retest. Headache was diagnosed according to the International Classification of Headache Disorders, 2nd edition. The results on vertical and horizontal VAS did not differ significantly in the different headache or chronic pain groups. For test-retest evaluation, effect sizes and Cohen's delta values were < 0.029 with < 1.5% change from test to retest (P < 0.01). Correlation coefficients were > 0.95. Bland-Altman analysis showed good agreement between vertical and horizontal scores with correlation coefficients > 0.84. A vertical VAS is equally valid as a horizontal VAS for registration of pain intensity in headache and non-headache patients.