Objectives: There are many potential ways that gout flares could be reported in clinical trials. The aim of this study was to describe the methods used to measure and report gout flare prevention outcomes in randomized controlled trials (RCTs). Methods: A systematic search of electronic databases was conducted. Articles published between 2008 and 2018 were included if they were RCTs or articles reporting on analyses of RCT data (i.e. open label extension studies) and reported the impact of an intervention on the prevention of flares in people with gout. The modified-Jadad scale was used to assess study quality. Methods used to measure and report gout flare outcomes were extracted and synthesised separately for studies of anti-inflammatory prophylaxis and urate lowering/other long term therapy. Results: A total of 38 articles were included, with 10 reporting outcomes for anti-inflammatory prophylaxis and 28 for urate lowering/other long term therapies. The overall quality score of all articles was good. There was marked heterogeneity across trials in gout flare definitions, data capture methods, reporting methods and time periods used to report flares. Anti-inflammatory prophylaxis studies used multiple methods to report gout flare outcomes (mean (SD) 4.3 (2.5) methods/article), while the majority of urate lowering/other long term therapy studies used a single method to report gout flare outcomes. The most common reporting method in anti-inflammatory prophylaxis studies was the mean number of gout flares per patient (n = =9 articles), and in urate lowering/other long term therapy studies was the proportion of patients with at least one gout flare (n = =22 articles). Only studies of anti-inflammatory prophylaxis therapy reported flare duration or pain during flare. Conclusion: There is wide variation in methods used to measure and report gout flare prevention outcomes in long-term RCTs. These findings highlight the need for standardized methods for studies in which gout flare prevention is an outcome of interest.