Turner's syndrome (TS) is a common disorder (1/2500 to 1/5000 female births) which is diagnosed at birth in approximately 20% of patients and during childhood or at puberty for the rest. Growth retardation is the most frequent clinical feature of TS, so we systematically searched for TS in female patients referred to our center because of short stature. Three hundred seventy-five female patients, 1 month to 18 yr old (mean +/- SD = 9(7/12) +/- 3(9/12), with growth retardation (less than -2 SD) and/or decreased height velocity were included in the study. Mean growth retardation was -2.57 SD +/- 0.79 (range: -1 to -7). Thirty-two percent of the patients had reached puberty. GH provocative tests were performed in 329 patients (87.7%), and 36 of these patients (11%) had impaired GH secretion (5 complete and 31 partial GH deficiency). TS was evaluated by Southern blot analysis of leukocyte DNA using a multiallelic polymorphic X chromosome marker (88% heterozygosity rate). Y chromosome PCR analysis was carried out if a pattern indicative of TS was obtained. Leukocyte DNA analysis produced an abnormal restriction pattern for 20 of the 375 cases (5.3%). There was a single hybridizing band in 13 cases, an allelic disproportion indicative of mosaicism in 6 cases, and 3 hybridizing bands in 1 case. One patient tested positive in the Y chromosome PCR analysis. Cytogenetic analysis showed 47 XXX trisomy in the patient with a 3-hybridizing-band pattern and confirmed the diagnosis of TS for 17 of the 19 suspected cases: 45 X: n = 7; 45 X/46 Xi(Xq): n = 4; 45 X/46 XX: n = 2; 46 Xi(Xq): n = 1; 45 X/46 Xr(X): n = 1; 45 X/46 XX/47 XXX: n = 1; 45 X/46 XY: n = 1. Cytogenetic analysis was normal (46 XX) for the 2 other patients. The TS phenotype is variable: dysmorphism is often missing or mild (particularly in cases of mosaicism), but growth is reduced in virtually all patients. Screening of 375 growth-retarded girls identified 18 cases of TS, of which 17 were diagnosed by molecular analysis. This incidence (4.8%) was significantly higher than the expected incidence in this population (0.8-1.6%: P < 0.001).