Objective: To investigate the long-term efficacy and safety of gonadotropin-releasing hormone analog (GnRHa) treatment in children with idiopathic central precocious puberty (CPP). Method: The protocol was registered with International Prospective Register of Systematic Reviews (CRD42018102792). PubMed, EMBASE and the Cochrane Library were searched for eligible comparative and single-arm studies. Results: We identified a total of 98 studies that included 5475 individuals. The overall risk of bias of the eligible studies ranged from critical to moderate. The overall quality of evidence for each outcome ranged from very low to moderate. Evidence-based comparative studies showed that GnRHa treatment increase final adult height (FAH, cm; studies = 4, n = 242; mean difference [MD] = 4.83; 95% confidence interval [CI], 2.32 to 7.34; I-2 = 49%) and decrease body mass index (BMI, kg/m(2); studies = 3, n = 334; MD = -1.01; 95% CI, -1.64 to -0.37; I-2 = 0%) in girls with idiopathic CPP compared with no treatment. The incidence of polycystic ovary syndrome (PCOS) did not significantly differ with and without GnRHa treatment (studies = 3, n = 179; risk ratio = 1.21; 95% CI, 0.46 to 3.15; I-2 = 48%). The evidence for other long-term outcomes was very weak to deduce the effects of GnRHa treatment. Further, limited evidence is available on its effects in boys. Conclusion: Compared with no treatment, evidence indicates that GnRHa treatment increase FAH and decrease BMI in girls with idiopathic CPP. GnRHa treatment did not evidently increase the risk of PCOS. However, evidence regarding other key long-term outcomes (such as infertility and malignant or metabolic diseases) was considered very weak to suggest the benefits or side effects of GnRHa treatment. Additional high-quality evidence is needed before firm conclusions can be drawn.