It is well known that high doses of corticosteroids can induce psychiatric disorders, especially the maniacal states. However there are only a few studies that investigate the effects of low and medium doses of such drugs used for a long period of time on the patient's mental health. The aim of the study was to investigate the prevalence and severity of affective disorders among the patients using up to 40 mg of corticosteroids (prednisone or equivalent). 54 patients during the corticosteroid therapy and 51 healthy controls were assessed with the use of the following questionnaires: Hypomania Checklist 16 (HCL-16), Beck Depression Inventory (BDI) and authors' questionnaire. The results were analysed using SPSS Statistics version 12.5. The results indicated statistically significant differences in the prevalence of hypomania and depression between controls and study group. There were no evident correlations between either the dose or the length of the therapy and the severity of affective disorders. The study has shown that the usage of corticosteroids doses below 40 mg does have an effect on the prevalence of affective disorders. The occurrence of hypomania and depression was more common among the study group. To assess correlations further studies are needed.