Two 10 cm visual analogue scales were compared with a 0-10 point numerical rating scale and a four-point verbal descriptive scale, in assessing pain severity in twelve patients with post-operative pain following removal of an impacted lower third molar. High correlations were shown between the pain scores from the two visual analogue scales and the numerical scale, but a lower correlation was obtained when the four-point scale was compared with the other scales. Analgesic efficacy was found to be dependent on the type of scale used. The 10 cm visual analogue scale was more sensitive than other pain scales and could discriminate between small changes in pain intensity.