Importance: Forehead reduction, or hairline lowering surgery, is becoming more popular as a cosmetic procedure for patients with disproportionately large foreheads. A large forehead can make a patient appear older, be masculinizing, and less attractive. Objective: To quantify reported outcomes in patients undergoing forehead reduction. Methods: We performed a systematic review and meta-analysis of adults undergoing forehead reduction. A review protocol was published in PROSPERO (CRD42020183366). A research librarian created search strategies in multiple databases. Abstracts and full texts were reviewed in duplicate. The Newcastle-Ottawa scale and Cochrane Collaboration Risk of Bias tool were used. Random effects meta-analyses were performed. The primary outcome was amount of reduction. Other extracted data included study type, location, sample size, scalp fixation method, incision, complications, follow-up time, percentage female, and age. Results: Our search strategy found 376 unique citations, and 8 studies were included. All eight were retrospective cohort studies, comprising 882 patients (range 5-525). Study quality was high, and risk of bias ranged from unclear to high. Four studies were included for meta-analysis, totaling 801 patients. Mean amount of reduction was 1.6 cm (95% confidence interval: 1.4-1.8). Complications included temporary and permanent alopecia, unacceptable scarring, persistent paresthesia, and hematoma. The pooled complication rate was 1% or less. Conclusion: Forehead reduction is associated with a low complication rate (<1%), and a mean lowering of 1.6 cm is reported. Future studies should report mean and standard deviation of reduction, and should follow patients for at least 12 months.