Introduction There are scarce data about the effect of metformin on lipid profile in patients with type 1 diabetes. Objectives The present study is the first prospective clinical trial evaluating the effect of combined therapy of metformin and insulin on the pool of oxidized and glycated low-density lipoproteins (LDL) in young patients with type 1 diabetes and concomitant obesity. Patients and methods A total of 33 obese patients with type 1 diabetes treated with intensive insulin therapy were randomized into a group where metformin was added. The remaining 19 patients continued to receive intensive insulin therapy (control group). In all patients, lipid profile and glycemia were assessed using routine laboratory tests. Oxidized and glycated LDL were measured using commercially available kits. Laboratory tests were performed at baseline and at a control visit after 6 months of treatment. Results A significant decrease in the levels of glycated hemoglobin, fasting plasma glucose, postprandial glucose, average glucose, triglycerides, glycated LDL, and body mass index was observed in the group receiving combined therapy. A similar decrease was not observed in the control group. The remaining lipid parameters were not changed during follow-up in any of th e groups. Conclusions Addition of metformin to intensive insulin therapy in young obese patients with type 1 diabetes results in a significant reduction of glycated LDL levels. This can be possibly explained by better glucose control, which improved insulin sensitivity of the peripheral tissues and reduced body mass in this patient group.