PURPOSE: Children experience painful invasive procedures very intensely. The aim of health professionals is to help children minimize this traumatic experience. The Simplified Faces Pain Scale (S-FPS) and Simplified Concrete Ordinal Pain Scale (S-COS) tools offer children the possibility of self-assessing their pain. This can then be the basis for tailoring pain relief to the child's individual need. The aim of this study is to present the validation procedure of the S-FPC, S-COS methods. DESIGN AND METHODS: 135 children aged 3-6 years assessed their pain using the self-reported S-FPS and S-COS methods at three consecutive times, and their results were compared with the commonly used Face, Legs, Activity, Cry, Consolability assessment scale. Intra-class correlations (ICC) were used to assess inter-rater agreement. Convergent validity was verified using Spearman's correlation coefficient. RESULTS: This study demonstrated good validity for both the S FPS and S-COS assessment tools. The ICC coefficient showed good inter-rater correlation. Spearman's correlation coefficient showed a strong correlation between the scales. PRACTICE IMPLICATIONS: It is not possible to clearly select a best method of pain assessment in preschool children. To choose the most appropriate method, it is necessary to take into account the child's cognitive development and preferences.