A successful pregnancy in a woman with Turner's syndrome with a 45,X/46,XX karyotype is described. The literature contains reports of a total of nine pregnancies in seven women with a 45,X karyotype and 56 pregnancies in 23 women with mosaicism and a 45,X cell line, as well as a 46,XX and/or 47,XXX cell line. Fifteen of the latter 56 pregnancies ended in spontaneous abortion (27 per cent), and four ended in the delivery of a stillborn child; 12 of the 37 liveborn infants (32 per cent) had a physical or mental abnormality, and 8 (22 per cent) had a chromosome abnormality. Three had Down's syndrome, and five had a 45,X cell line. Due to the relatively high (8 per cent) incidence of Down's syndrome among liveborn infants of women with Turner's syndrome, amniocentesis for fetal karyotyping should be advised.