Objective The frequency of Y-chromosome material is high in Turner syndrome (TS), but the ocurrence of gonadoblastoma seems to be low. We performed a study to evaluate whether DNA analysis might be a useful tool in the evaluation of patients with TS. Subjects Unrelated patients with TS (n = 52) of Venezuelan mestizo ethnic origin were diagnosed by cytogenetic analysis as having TS. Methods Clinical assessment, karyotyping, endocrine evaluation, fluorescence in situ hybridization, and polymerase reaction chain analysis of the Y-chromosome loci. Results We found that 7.69% (4 of 52) patients with TS had Y-chromosome material. A low occurrence of gonadoblastoma was also found (2 of 52 [3.85%]). Two patients showed a 45,X/46,XY karyotype, and gonadoblastoma in the gonadal biopsy specimen was not found. Two patients had no Y chromosome on initial karyotype; they were positive on lymphocyte DNA to Y-sequences specific. Both patients (45,X) had bilateral gonadoblastoma. The four patients with Y-chromosome material in peripheral blood lymphocytes had Y-chromosome sequences on gonadal DNA. Fluorescence in situ hybridization confirmed their Y-chromosome origin. Conclusions Our results suggest that the detection of Y-chromosome material should be carried out in all patients with TS and not be limited to patients with TS with cytogenetically identifiable Y chromosome and/or virilization. (J Pediatr 2003;142:336-40)