A total of 186 girls with clinical signs of Turner's syndrome were cytogenetically studied. From this total, 125 (67.20%) had abnormal and 61 (32.80%) normal karyotypes. Among the patients with abnormal karyotypes, 68 had negative sex chromatin (54.40%) and 57 positive sex chromatin (45.60%). Chromosomal studies in chromatin-negative patients allowed us to detect 44 karyotypes 45,X, 20 structural X anomalies (14 rings, 4 deletions for the long arm, 2 deletions for the short arm) and 4 patients with 45,X/46,XY mosaics, while chromosomal studies in chromatin-positive patients revealed 57 abnormal and 61 normal karyotypes. The isochromosome for the long X arm was more frequent, either in pure line or in mosaicism, than the 45,X/46,XX mosaic. From the 61 patients with normal karyotypes, 21 had significative short stature (under the 3rd percentile) as the main feature, with the bone age equal to, or advanced for chronological age. The remaining 40 patients had, in addition, other typical features of Turner's syndrome. Although the possibility of a not detected mosaic cannot be discarded, its absence would suggest a genetic etiology.