Aims: To investigate whether karyotype, mid-childhood (6–10 years) follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, and ultrasound ovary visualization results can be used as indicators of spontaneous puberty in Turner syndrome (TS). Methods: The analysis was based on clinical and biochemical data from 110 TS girls aged >13 years at the end of the study (1,140 visits between 1996 and 2015). The study population was divided according to karyotype: 45,X and non-45,X. Results: The mean age ± standard deviation at diagnosis was 10.7 ± 4.0 years, and the follow-up duration was 5.9 ± 3.3 years. Spontaneous puberty was confirmed in 48% and menarche in 20% of the subjects, less frequently in 45,X girls. The mean age at Tanner stage B2 was 13.7 ± 2.4 years and that at menarche 14.2 ± 1.7 years, regardless of the karyotype. The median FSH level at 6–10 years was 8.16 IU/L, which was significantly lower than <6 years and >10 years. The median LH level at 6–10 years was 0.35 IU/L, which was lower than >10 years. The chance of spontaneous menarche was decreased in girls with FSH ≥6.7 IU/L between 6 and 10 years. Conclusions: Although spontaneous puberty and menarche occur more frequently in non-45,X girls, the karyotype cannot be used to predict them. However, the chance of spontaneous menarche can be predicted based on gonadotropin cut-off values. There was no correlation between ultrasound ovary visualization results and spontaneous puberty.