Results are reported of a cytogenetic study on 165 patients with Turner syndrome, based on sex chromatin and karyotype tests. We found that the karyotype 45,X is present only in 54.54% of the cases in homogeneous form and in about 14% of the cases in mosaic form associated with a normal clone 46,XX or, rarely, also with a clone 47,XXX; in the other cases X structural anomalies and different kinds of mosaic forms are present. We also found 5 pregnancies in 2 patients: only 2 daughters were born and alive, the first was normal and the second presented the same karyotype and clinical picture of her mother.