Accurate assessment of renal function is of key importance, given its prognostic value. However, gold standard measures are cumbersome, and serum creatinine itself is an insensitive predictor, especially in renal transplant recipients. Though GFR-estimating formulae have been relied upon, they do have their own limitations. Nevertheless, renal biomarkers such as neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C, among others, are now emerging as potentially useful indicators of GFR. We aimed to evaluate the diagnostic performance of NGAL versus cystatin C and eGFR using CKD-EPI, MDRD and cystatin C in renal transplant recipients and non-transplant CKD patients. We found a significant correlation between NGAL, serum creatinine, cystatin C and eGFR. The latter parameters were also strong predictors of serum NGAL levels. However, performance of NGAL, based on receiver operating characteristic curves, was inferior to that of the reference tests. It appears that in renal transplant recipients NGAL correlates well with cystatin C and eGFR, most strongly with cystatin-based formula. Though this suggests potential use of NGAL as a screening test, its weaker diagnostic performance raises some concern about its clinical usefulness. Larger studies are needed to explore this further.