We evaluated the possibility of anticipating spontaneous puberty in peripubertal Turner girls, in order to plan substitutive estrogen treatment. In the 24 patients studied, spontaneous puberty was seen in 4/11 girls with 45 XO karyotype, 5/5 with mosaicisms, 1 out of 2 with structural aberrations of the X chromosome and 0 out of 6 with Xq isochromosomes. When considering sonographic findings, the 6 girls with normal ovaries and 4/9 of those with intermediate ovarian appearance showed spontaneous puberty; the remaining 5 with intermediate ovaries and 9 with streak gonads did not undergo spontaneous puberty. Gonadotropin secretion was normal in girls with normal ovaries, moderately elevated in patients with intermediate ovarian appearance, and very high in those with streak gonads. The prognostic value of sonography and gonadotropins is particularly important in girls with intermediate ovaries. Therefore these evaluations should be performed at peripubertal age in patients with Turner's syndrome to elucidate the degree of ovarian insufficiency.