Background: 'Horizontal violence' refers to hostile, aggressive, or harmful behaviour between peers. Nurse educators and managers who support newly qualified nurses should be aware of horizontal violence in the workplace when directed towards this professional group. The prevalence of horizontal violence in newly qualified nurses has not been subject to a systematic review. Aim: The aim of this systematic review was to estimate prevalence of horizontal violence in newly qualified nurses in their first year of practice. Methods: A systematic search was undertaken with the following databases on October 2018: AMED, CINAHL, CENTRAL, EMBASE, MEDLINE, ERIC and PsychINFO. An updated search was undertaken on August 12, 2020. Observational and experimental studies were included. Two researchers independently completed title, abstract and full-text screening. Nine studies were finally included in the review. Risk of bias was determined using the Joanna Briggs Institute critical appraisal tool. Findings.: Included studies were cross-sectional in design and horizontal violence was determined using nine different self-report measures. Reported rates of horizontal violence ranged from 7% to 73%. All included studies were rated as having a moderate risk of bias. Discussion: The broad range of prevalence estimates is likely explained by the use of different measures in included studies and the sources of bias. It is unclear if horizontal violence is common in nurses in their first year of practice. Further research that addresses the sources of bias we have identified is justified. Conclusion: There is considerable variation in prevalence estimates of horizontal violence in nurses in their first year of practice