["Due to increased use of imaging techniques, adrenal incidentalomas are frequently detected. The majority are non-hyperfunctioning adrenocortical tumors. We have previously shown that expression of the gene CYP17, coding for the enzyme in the cortisol pathway, correlates with cortisol release from adrenocortical tumors in vitro. The aim of this study was to compare clinical data with mRNA expression of CYP17 and CYP11B1 in adrenocortical tumors from patients with and without Cushing's syndrome and to identify adrenal tumors that may cause subclinical Cushing's syndrome.", 'A retrospective study of 34 patients undergoing adrenalectomy due to an adrenal tumor.', 'Clinical data were collected. In the adrenal gland the mRNA expression of the genes CYP17 and CYP11B1 was studied with in situ hybridisation technique.', "The median ratio of CYP17/CYP11B1 expression in tumors from patients with Cushing's syndrome was significantly higher than the median ratio in the non-hyperfunctioning tumors. Tumors from 2 patients with subclinical Cushing's syndrome had ratios within the upper range for non-hyperfunctioning tumors."] Does increased ratio of mRNA expression of the genes CYP17 and CYP11B1 indicate autonomous cortisol production in adrenocortical tumors?