Abstract Aim: To examine what is known about evidence and validity of today´s pain assessment tools for children 1-12 years old, and about when to use these tools. Background: Assessment of pain in the pediatric patient is difficult. Children do not have fully developed cognitive and verbal skills and therefore express pain differently than adults. Still, accurate and good pain assessment in children is important because pain causes severe stress reactions, with potential adverse effects both in the short and long term. Pain may also have a huge impact on the patient's quality of life. Experiences gained early in life may affect help-seeking behavior and use of health care resources throughout life. Children, especially those who are preverbal or nonverbal, are at high risk for having their pain over¬looked and its treatment subsequently disregarded. Various pain assessment tools have been developed to help healthcare professionals detect, interpret, and treat children's pain. Methods: PubMed was searched 24th January 2019 for papers on development and validation of pediatric pain assessment tools. Both systematic reviews and primary studies were included. Different combinations of search terms were used to obtain as many relevant papers as possible. All articles detected were initially evaluated based on their title and abstract. Papers appearing relevant were subsequently evaluated by reading their full text. Some papers found outside the PubMed search were included, as were information from relevant and reliable websites. Results: Of 1155 articles identified in the primary search, 63 were included in this review. Twenty more were included from other sources and relevant websites. Eight articles and websites were included exclusively because they contained relevant information about how to evaluate pain assessment tools. Pain evaluation tools included in this study were self-assessment tools (Oucher scale, WBFPRS, FPS, FPS-R, CAS, RPS, NRS, VAS) and observational tools (FLACC, CHEOPS, CHIPPS, TPPPS, OPS, PEEPS, M-PEPPS, BOPS, AHTPS, EVENDOL). Conclusions: Self-reporting tools are often advocated as the primary method for measuring pain intensity in children, but there are disagreements about at what ages children are able to use them. Observational pain tools should be used if the child is unable to self-report. There are many pain assessment tools available, but more research is needed to better define when, for which groups, and for what type of pain the various pain assessment tools should be used.