Rationale and objectives: Oxidative stress is increased in chronic kidney disease (CKD) patients and end-stage renal disease (ESRD) patients undergoing dialysis treatment. Coenzyme Q10 (CoQ10) is a ubiquitous and strong antioxidant. Role of CoQ10 is not fully evaluated in renal patients. We aimed to investigate the relationship of CoQ10 with oxidant and antioxidant system markers in patients with renal disease. Material and methods: Forty patients with CKD (stages 35) who were managed conservatively without dialysis treatment, 40 hemodialysis, and 60 chronic ambulatory peritoneal dialysis (CAPD) patients were included in the study. Biochemical and whole blood analyses were done using hospital auto-analyzers from stored samples. Serum CoQ10, malondialdehyde (MDA), superoxide dismutase (SOD), and antioxidant activity (AOA) levels were determined. Main findings: There was no difference among the groups in terms of serum CoQ10 levels. However, other components of antioxidant system, namely, SOD and AOA were significantly higher in CAPD patients when compared to CKD patients. MDA levels were not significantly different among the groups. Principal conclusion(s): The results of this study showed no difference among CKD, CAPD, and hemodialysis patients in terms of serum CoQ10 levels. © 2011 Informa Healthcare USA, Inc.