One of the characteristic symptoms in girls and women with Turner syndrome (TS) is ovarian failure with infertility. Puberty starts spontaneously in 15% to 30% of girls with this syndrome but less than 5% reach menarche with the possibility of becoming pregnant because ovarian follicles secreting estrogen disappear prematurely. In a prior study, the investigators cryopreserved biopsy specimens from ovarian cortical tissue of adolescent girls with TS and found remaining follicles in 8 of 10 girls. This study investigated clinical and laboratory parameters that could help identify which girls with TS are likely to benefit from freezing of ovarian tissue to preserve fertility. The study subjects were 57 girls with TS, aged 8 to 19.8 years who had been referred to a fertility unit by 25 pediatric endocrinologists in Sweden. Ovarian cortical tissue was biopsied laparoscopically for follicle counts and cryopreserved. Parameters analyzed included karyotype, age at biopsy, spontaneous onset of puberty and menarche, number of follicles, and serum concentrations of follicle stimulating hormone, luteinizing hormone, and anti-Mullerian hormone. Among the 57 girls in the study, ovarian biopsy was feasible in 47, and follicles were identified in 15 (26%). Follicles were found in 6 of 7 (86%) girls with mosaicism, in 6 of 22 (27%) with structural chromosomal abnormalities, and in 3 of 28 (10.7%) with karyotype 45X. Signs of spontaneous onset of puberty were found in 19 girls, 11 of whom (58%) had follicles in the tissue. Menarche had been reached spontaneously in 13 girls; of these, 8 (62%) had follicles. Despite a high-negative predictive value for finding follicles in girls below 12 years, age was not a significant factor. These findings show that girls with TS who have the highest likelihood of having remaining follicles are those with mosaicism, spontaneous onset of puberty, and normal hormone concentrations.