There are few reports of an association between Turner syndrome (TS) and 21-hydroxylase deficiency. However, this association is more frequent in some populations. The aim of this study was to evaluate the incidence of 21-hydroxylase deficiency in patients with TS in our population. 21-hydroxylase deficiency was evaluated in 44 TS cases with 45X (n=20) and 24 mosaic cases. A standard dose adrenocorticotropic (ACTH) stimulation test (Synacthen, Novartis, Basel, Switzerland) was performed, and 17 hydroxyprogesterone (17OHP), dehydroepiandrosterone sulfate (DHEAS) and cortisol responses were evaluated. Patients with increased 17OHP responses in the stimulation test also underwent 21-hydroxylase gene analysis. The mean age was 14.6±4 (2.6–22.4); 37 patients were on growth hormone (GH) treatment. Nine patients were at prepubertal stage, whereas 35 were pubertal (24 on gonadal steroids and 11 spontaneously). Six patients were obese. Only one of our patients had a level of 7.5 ng/mL of 17OHP, and there was no mutation found in congenital adrenal hyperplasia (CAH) genetic analysis. In other cases, peak 17OHP levels were ≤6 ng/mL. The mean peak 17OHP was 2.62±1.48 (1.19–7.5) ng/mL, the cortisol level was 37.6±8.43 (23.9–56.2) μg/dL and the DHEAS was 135.2±87.3 (15–413) μg/dL. The increased mean basal and peak cortisol levels (20.5±10.2 and 37.6±8.4 μg/dL) were remarkable findings. Whereas basal cortisol was above 20 μg/dL in 38.7% of patients, exaggerated results up to 56.2 μg/dL were obtained in peak cortisol levels. The basal and peak 17OHP cortisol levels were not correlated with the presence of puberty, chromosome structure, gonadal steroid use, obesity or growth hormone use. This trial suggested that 21-hydroxylase deficiency was not common among patients with TS in our population. Adrenal function should be assessed, at least in the presence of clitoral enlargement in patients with TS, particularly if their karyotype does not contain a Y chromosome.