Sudden sensorineural hearing loss is usually treated with systemic glucocorticoids. Intratympanic injections of glucocorticoids offer a possibly equivalent treatment alternative, avoiding adverse systemic effects on blood glucose. We, therefore, investigated the extent to which different doses of systemic glucocorticoid therapy affects blood glucose levels. We conducted a retrospective analysis of treatment courses in 179 patients from the Departments of Otorhinolaryngology, Ophthalmology and Dermatology who underwent short-course systemic glucocorticoid therapy. Patients were subdivided into three groups on the basis of their cumulative prednisolone dose from days 1 to 3 (Group 1: <750 mg; Group 2: 750-1,499 mg; Group 3: >1,499 mg); in addition, a distinction was made between diabetic and non-diabetic patients. Among the non-diabetic patients on days 2-4, diabetic levels of fasting blood glucose were detected significantly more often (P < 0.01) in Group 3 (67 %) than in Group 1 (28 %) and Group 2 (21 %). Furthermore, there was a highly significant mean Pearson correlation (r = 0.329; P < 0.01) between blood glucose levels and glucocorticoid dose. This correlation was even more pronounced in the diabetic patients (r = 0.51; P = 0.02). In this category, hyperglycemia was detected in 40 % of patients in Group 1, 63 % in Group 2 and 100 % in Group 3. The prevalence of glucocorticoid-induced hyperglycemia during systemic therapy is high and rises as the dose increases. This should be kept in mind when choosing the dosage. Besides, it should also be considered that even short-term hyperglycemia presents possible health risks and the risk of inducing diabetes. This is especially of interest as intratympanic therapy offers a possible alternative to the systemic application.