Because creatinine is an unreliable variable describing kidney function, the search for a new and sensitive marker of kidney function is underway. Neutrophil gelatinase-associated lipocalin (NGAL) has been recently proven useful in the quantitation of chronic kidney disease (CKD). The aim of the study was to assess the prevalence of chronic kidney disease using estimated glomerular filtration rate (eGFR) and creatinine clearance according to different formulas and measurements of cystatin C and serum NGAL. One hundred sixty-nine prevalent heart transplant recipients in relation to age (younger and older than 65 years of age) were studied. Serum NGAL, cystatin C, creatinine, and eGFR were evaluated in all patients. Elderly heart recipients had significantly higher cystatin C and serum NGAL and lower eGFR than their younger counterparts, despite not having a statistically different serum creatinine. In the group of 27 elderly recipients, according to the Cockcroft-Gault formula, 22 patients had stage 3 CKD and 4 had stage 4 CKD; according to the Modification of Diet in Renal Disease (MDRD) Study formula, 5 had stage 2 CKD, 15 had stage 3 CKD, and 7 had stage 4 CKD; according to the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula, 5 had stage 2 CKD, 15 had stage 3 CKD, and 7 had stage 4 CKD; and according to the calculation of 24-hour creatinine clearance, 5 had stage 2 CKD, 16 had stage 3 CKD, and 6 had stage 4 CKD. The prevalence of CKD in the elderly population was as high as 81% (MDRD, CKD-EPI, creatinine clearance) to 100% (Cockcroft-Gault formula), whereas in the younger population of heart transplant recipients the prevalence of CKD ranged from 56.3% to 77.5%. Serum NGAL could be a sensitive marker of kidney function, particularly in elderly patients.