Background and objectives: School bullying is a growing problem. The current study is aimed at culturally adapting and assessing the psychometric properties of a brief scale to measure bullying.Material and methods: A cross-cultural adaptation of the brief scale Adolescent Peer Relations Instrument-Bullying (APRI) was performed using the translation and back-translation technique. The Spanish version of APRI questionnaire was administered to a sample of 1,428 schoolchildren aged 12-14 years in the region of Mar Menor in Murcia (Spain). Exploratory factor analysis, with oblique rotation, was used to assess the validity of the internal structure, the Cronbach's alpha to analyse their consistency, and the Kruskal-Wallis test to check their ability to discriminate between subjects with varying degrees of bullying according to Kidscreen-52 scale of social acceptabilityResults: Two factors were identified in the adapted version of APRI (physical victimisation and verbal/social victimisation), similar to those in the original scale. The questionnaire has high internal consistency (Cronbach's alpha = 0.94) and discrimination capacity (P < 01), with significant effect sizes between degrees Of bullying.Conclusions: The internal structure of the APRI Spanish version is similar to the original, and its scores confirm high reliability and construct validity. Further studies need to be performed with broader age ranges and confirmatory analysis techniques, to ratify the equivalence of the adapted version with the original version (C) 2015 Asociacion Espanola de Pediatria. Published by Elsevier Espana, S.L.U. All rights reserved.