The accurate assessment of pain in children constitutes a challenge for health professionals and, in the case of young children, parents are generally the main source of information. The objective of this study was to validate and to compare three pain scales in preschool children and their parents. A total of 104 children between 4 and 6 y of age and their parents participated in the study while undergoing an immunization procedure in the outpatient department of a tertiary pediatric care hospital. Three pain scales were used, the McGrath Facial Affective Scale (FAS), the Hester Poker Chip Tool (HPCT) and the Multiple Size Poker Chip Tool (MSPCT). There were 47 (45%) boys and 57 (55%) girls, with 54 (52%) 4-y-olds, 34 (33%) 5-y-olds and 16 (15%) 6-y-olds. Twenty-eight children (27%) had memories of pain experienced during a former hospitalization. Correlations were very high both in children (r = 0.78) and their parents (r = 0.96) when comparing immunization pain scores obtained from the HPCT versus the MSPCT. Correlations between McGrath's FAS and HPCT or MSPCT ranged from r = 0.34-0.43 in children and r = 0.38-0.39 in parents. There was a good correlation between parents and children during the immunization procedure on all three scales, with the highest correlation using the FAS (r = 0.76), followed by the MSPCT (r = 0.69), and the HPCT (r = 0.66). Subgroup analyses based on the criteria of age, sex and previous hospitalization showed no consistent relationship. Parents tended to underestimate their child's pain when using HPCT or MSPCT. It seems that both HPCT and MSPCT measure a similar dimension of pain, whereas the FAS addresses a different aspect of pain. Although parents play an important role in their child's pain assessment, they tend to underestimate the intensity of pain when using HPCT or MSPCT.