BACKGROUND: The risk of steroid-induced hyperglycemia is debated, and methylprednisolone is still used during spinal surgery. We have compared the blood glucose level in patients with metabolic syndrome treated with or without methylprednisolone. METHODS: This study was conducted in 68 adult patients who underwent elective spine surgery. Patients were classified into the following groups: methylprednisolone group (n = 39, group M), placebo group (n = 29, group P), group M patients with metabolic syndrome (n = 17, group MM), and group P patients without metabolic syndrome (n = 21, group NMP). Before and after injection of either 125 mg methylprednisolone or a placebo, we consecutively checked the blood glucose level every 30 minutes up to 4 hours. RESULTS: The blood glucose level was significantly increased in group M patients as compared to group P patients. The blood glucose level was more significantly increased in group MM as compared to group NMP patients. The increased blood glucose levels over 4 hours were 50 mg/dl in group MM and 35 mg/dl in group NMP patients. CONCLUSIONS: We recommend that close monitoring of the blood glucose level up to several hours after injection of a steroid should be seriously considered during spine surgery, particularly in patients with metabolic syndrome.