Abstract Background There is no consensus for when publicly funded breast reduction is indicated and recommendations in guidelines vary greatly, indicating a lack of evidence and unequal access. The primary aim of this review was to examine risks and benefits of breast reduction to treat breast hypertrophy. Secondary aims were to examine how the studies defined breast hypertrophy and indications for a breast reduction. Methods A systematic literature search was conducted in PubMed, MEDLINE All, Embase, the Cochrane Library, and PsycInfo. The included articles were critically appraised, and certainty of evidence was assessed using the GRADE approach. Meta-analyses were performed when possible. Results Fifteen articles were included; eight reporting findings from four randomised controlled trials, three non-randomised controlled studies, three case series, and one qualitative study. Most studies had serious study limitations and problems with directness. Few of the studies defined breast hypertrophy. The studies showed significantly improved health-related quality of life and sexuality-related outcomes in patients who had undergone breast reduction compared with controls, as well as reduced depressive symptoms, levels of anxiety and pain. Most effect sizes exceeded the reported minimal important difference for the scale. Certainty of evidence for the outcomes above is low (GRADE ⊕ ⊕). Although four studies reported significantly improved physical function, the effect is uncertain (very low certainty of evidence, GRADE ⊕). None of the included studies reported data regarding work ability or sick leave. Three case series reported a 30-day mortality of zero. Reported major complications after breast reduction ranged from 2.4 to 14% and minor complications from 2.4 to 69%. Conclusion There is a lack of high-quality studies evaluating the results of breast reduction. A breast reduction may have positive psychological and physical effects for women, but it is unclear which women benefit the most and which women should be offered a breast reduction in the public healthcare system. Several priorities for further research have been identified. Pre-registration The study is based on a Health Technology Assessment report, pre-registered and then published on the website of The Regional HTA Centre of Region Västra Götaland, Sweden.