Background: Pain control is a priority in palliative care.Intensity is one of the major elements in pain assessment,and should be evaluated through scales, which enhance itsobjectivity. The knowledge and adequate use of the existinginstruments for pain evaluation is essential.Aim: Identification of valid and reliable pain assessmentinstruments.Methods: A systematic literature review was undertaken, onPubmed® database. Papers published on the period between2000 and 2015, written in English, French, Spanish andPortuguese were included. Results: 3217 articles were identified, after exclusion andinclusion criteria and abstract review, 103 papers wereselected for full text analysis. 16 different pain assessmentinstruments were identified and characterized. Heterogeneityin pain assessment scales was found, and these could bebroadly divided in: one-dimensional instruments, multi-dimensional and quality of life scales.Discussion: An absence of consensus regarding painevaluation scales was identified. The lack of standardizationof assessment tools renders the comparison of efficacy andeffectiveness of pain controlling interventions particularlydifficult. However, it was possible to make an extensive surveyof pain assessment scales, identifying the psychometriccharacteristics of each of the identified scales, country, andtype of study, context, target population and number ofcitations.This study confirms the need for standardization of painassessment scales, by the health services, in compliance withthe World Health Organization recommendations for PalliativeCare.