This study explored whether global unidimensional self-report pain scales based on facial expression help children separately estimate the sensory and affective magnitude of post-operative pain. Ninety paediatric elective surgery patients (in two age groups: 5-9 and 10-15 years) used each of four scales to estimate pain intensity and pain affect during the first 2 days after surgery. The four scales were: Faces Pain Scale (FPS), Facial Affective Scale (FAS), and the Coloured Analogue Scale (CAS) (one for intensity and one for unpleasantness). As hypothesised, ratings on the FPS correlated more highly with analogue scale ratings for intensity than for unpleasantness, whereas ratings on the FAS correlated more highly with those on the analogue scale for unpleasantness than for intensity. Factor analysis indicated that although all measures loaded on a single dimension of distress, there was an additional weaker factor corresponding to a unique contribution of the FAS. No systematic age effects were observed. It was concluded that the FPS and the FAS may partly measure different aspects of the postoperative pain experience in children, although shared instrument variance may obscure true estimates of covariation in ratings of intensity and affective magnitude. The clinical relevance of the present results remains to be determined. © 2002 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. All rights reserved.