Real-time ultrasonography was performed in 142 patients with Turner syndrome, aged 0.57 to 21 years, with different karyotypes (45,X [4896], X mosaicism [17%], and X structural abnormalities [35%]). Ovarian and uterine volumes were calculated and the data collected in a mixed longitudinal and cross-sectional mode. Thirty-eight patients were followed longitudinally during pubertal age (10 to 18 years bone age) for ovarian data. Patients with Turner syndrome were divided into two groups according to the presence or absence of detectable ovaries. Patients with Turner syndrome with detectable ovaries showed the first increase in ovarian volume at about 9 years of bone age; this increase was continuous and more evident only after 14 years of age and appeared later than in control subjects. When followed longitudinally during puberty, the ovaries showed a hormonal function in some cases. Girls with X mosaicism had the highest percentage of bilateral detectable ovaries and the greatest total ovarian volume; about 50% of them had spontaneous breast appearance and 38.5% had spontaneous menarche. They showed also the lowest gonadotropin levels, when bilateral ovaries were present during puberty. On the contrary, patients with the 45,X karyotype had the lowest percentage of detectable ovaries, ovarian volume, and spontaneous breast appearance. In our patients with Turner syndrome, uterine measures increased significantly with age and this was more evident in subjects with detectable ovaries after 13 years of bone age. Compared with control subjects, they showed significantly lower uterine measures, and patients with X mosaicism had greater and more progressive increments. In conclusion, pelvic ultrasonography in Turner syndrome is particularly useful in detecting ovaries and their possible increase in volume. These data, linked with karyotype pattern and gonadotropin levels, have prognostic value in predicting the future sexual development of these patients.