: Early sport specialization, involving intensive focus on a single sport for greater than 8 months per year at a prepubescent age, has become increasingly common in young athletes. While early sport specialization is often regarded as essential for success, there is growing concern that the potential risks to young athletes may outweigh the perceived benefits. Although numerous studies have explored early sport specialization, there has been no summative review on the topic in regard to the comprehensive impact on outcomes in these athletes. This study aims to systematically review the literature to determine the impacts of early specialization on injury, function, performance, sport success, and psychological outcomes. : A review of Medline (PubMed) was conducted to search for studies relating to early sport specialization in pediatric patients (time of specialization < 18 years old) and outcomes. Extracted information included injury outcomes with a focus on overuse injuries, functional outcomes, performance outcomes, sport success, and psychological outcomes. For studies that reported relevant statistics, < 0.05 was considered statistically significant. All studies were described qualitatively. : An initial search resulted in a total of 826 studies. After applying inclusion and exclusion criteria, 93 studies were included. A total of 62,327 athletes were included in the study. The average age of study participants was 15.9 years, with an average age at specialization of 11.6 years. Early sport specialization was associated with increased risk of injury, worse functional and physical performance, decreased or no benefit to sport success, and poor psychological outcomes. : Early sport specialization was associated with increased risk of injury and negative impacts on functional and physical performance measures. There was also no clear advantage regarding sport success. Early sport specialization was linked to harmful effects on athlete psychological well-being. Late specialization, multisport participation, and following training volume guidelines can aid in mitigating these risks.