BACKGROUND: Girls with Turner syndrome (TS) have a high incidence of primary ovarian insufficiency. Recent data show rates of spontaneous thelarche (ST) of 38% and spontaneous menarche (SM) of 15-16%, with higher rates in those with mosaicism. SUMMARY: We systematically reviewed the literature for evidence regarding rates of ST and SM in TS and evaluated rates based on the type of chromosomal mosaicism. We searched MEDLINE via PubMed, Embase, and the Cochrane Database of Controlled Trials. Reference lists were screened. Studies reporting outcomes of ST and SM in girls with TS, diagnosed by genetic analysis, were included. Data was collected regarding study design, cohort type, cohort age, the number of participants with ST and SM, the individual age at diagnosis of ST and SM, the mean age of patients with ST and SM, sample size, the number of participants with secondary amenorrhea, and karyotype. Key Messages: In total 2,699 patients were assessed for ST and 2,890 for SM from 43 articles. Overall the rates of ST were 32% (95% CI 26.4-38.9) and SM 20.8% (95% CI 19.3-22.4). Girls with X monosomy had the lowest rates of ST (i.e., 13%; 95% CI 8.7-19.7) and SM (i.e., 9.1%; 95% CI 7.3-11.3). Girls with 45,X/47,XXX had the highest rates of ST (i.e., 88.1%; 95% CI 62-97.1) and SM (i.e., 66.2%; 95% CI 49.3-79.6). CONCLUSIONS: Rates of ST and SM differ by karyotype in TS. When counseling patients, the karyotype should strongly influence discussions regarding pubertal development and the future reproductive potential.