Objective: Renal tubular acidosis (RTA) is a clinical manifestation that occurs with insufficiency in restoring bicarbonate or disruption in hydrogen ion elimination as a result of a disruption in tubulus functions, causing normal anion gap-opening metabolic acidosis. In the present study, we aimed to investigate the prevalence of RTA in the largest systemic lupus erythematosus (SLE) patient population to date. Materials and Methods: SLE patients, who were followed up in 2 different healthcare centers, were included. Patients with metabolic acidosis (pH <7.35 and HCO3 <22 mEq/L) in venous blood gas analysis were determined. The serum and urine anion GAP of these patients were estimated, and the urine pH was assessed. RTA presence was evaluated as metabolic acidosis with a normal serum anion gap and a positive urine anion GAP. Results: A total of 108 patients were included in the present study. The mean age of the patients was 41.5 +/- 1.2 and 87% were female. The SLE diagnosis duration was 75 +/- 5 months. The mean creatinine value was 0.6 +/- 0.1 mg/dL and the mean eGFR was 111 +/- 2 mL/min. According to the blood gas analysis, 18 patients (16.7% of the total) had RTA. Sixteen of these patients had type 1 RTA and 2 had type 2 RTA; type 4 RTA was not determined in any of the patients. Conclusion: RTA should be considered in SLE patients even if they have normal eGFR values. This is the largest study to examine the prevalence of RTA in SLE patients in the literature.