OBJECTIVE: Poor glycemic control increases the risk of diabetes complications. Serum cancer antigen 125 (CA125) has been associated with diabetes status in patients with type 2 diabetes mellitus (T2DM). Our aim was to focus on the association between serum CA125 and renal impairment in patients with T2DM. METHODS: Retrospective study included 151 patients with T2DM, with review of clinical and laboratory data. RESULTS: =0.025). CONCLUSIONS: Serum CA125 levels are positively correlated with urinary microalbumin and 24-hours urinary protein in T2DM patients; renal impairment may increase serum CA125 levels in T2DM patients.