Background/Aims: Cardiac surgery and diabetes are major causes of acute kidney injury (AKI). We aimed to investigate the value of urinary neutrophil gelatinase-associated lipocalin (NGAL) and serum cystatin C, as early biomarkers for prediction of AKI in diabetic and non-diabetic adult patients undergoing cardiac surgery. Methods: 15 non-diabetic and 15 diabetic adult patients undergoing cardiac surgery were enrolled. Peri-operative clinical and laboratory variables were recorded. Urinary NGAL, serum cystatin C, serum creatinine (Cre) and blood urea nitrogen (BUN) were evaluated. Results: AKI was detected in 4 patients in non-diabetic group and 12 patients in diabetic group. Urinary NGAL levels of diabetic and non-diabetic patients and serum cystatin C levels of diabetic patients exceed upper normal limits or cutoff values much earlier than BUN and Cre. cystatin C levels of non-diabetic patients remain unchanged. Cystatin C and NGAL levels of patients meeting AKI criteria and NGAL levels of patients not meeting AKI criteria exceeded upper normal limits or cut off values much earlier in than BUN and Cre. Conclusions: Measurement of cystatin C level in both diabetic and non-diabetic patients may reveal AKI earlier than NGAL and BUN. In diabetic patients, measurement of urinary NGAL and serum cystatin C levels may indicate AKI signs earlier than BUN and Cre.