We undertook to explore the validity of pain measurement tools for use in children in the postoperative period. The general approach was to determine the extent to which a measurement tool conformed with the clinical expectations about pain in the postoperative period; namely, that pain is low prior to surgery, increases following surgery, decreases with pain medication and decreases over time following surgery. In children aged 6 months to 3 years, we evaluated the CHEOPS and Observer pain scales. In children 3-6 years of age, we used the CHEOPS, Observer and Faces scale. In children 6-12 years of age, we studied the CHEOPS, Faces and visual analogue scales. In all instances, each of the scales conformed with the clinical expectations about pain following surgery. In addition, these scales were correlated with each other. Within the limitations of the measurement techniques used, these data provide support for the validity of the measurement tools evaluated.