Aim. To study the effect of selenium on adrenocortical function in patients taking glucocorticosteroids (GCS) long. Subjects and methods. The study included 56 patients who had been long taking oral GCS for the underlying disease. Adrenocortical function was evaluated by a short synacthen test; adrenal insufficiency (mean cortisol level 8.2 µg/dl) was identified in 52 patients. A study group of patients (n=35) was given selenium 200 µg/day. A control group (n=17) with the detected adrenal insufficiency did not take it. All the patients (n=52) continued to receive standard therapy for the underlying disease, including oral GCS. Results. Adrenal function was reexamined 6 months later; the two paired-samples t-test indicated a statistically significant increase in cortisol levels up to 23.20±4.2 µg/dl (p≤0.05) in the patient group receiving selenium in addition to the basic therapy. In the control group, the function did not recover (cortisol levels were 8.6 and 9.8 µg/dl at baseline and at 6 months, respectively; p≤0.05). Conclusion. The experience with selenium 200 µg/day given long to patients with adrenal insufficiency caused by the long-term use of GCS shows that the agent is effective in recovering adrenocortical function.