Introduction: The estimation of renal function is an important component of hospital care. To do this, estimates are usually used, based on serum creatinine levels. The most widely used equations are MDRD and Cockcroft-Gault. Objective: To evaluate the correlation of the Cockcroft-Gault and MDRD equations with the creatinine clearance value, based on 24-hour urine collection. Methods: In order to carry out this study, the records of the Clinical Pathology Service of Hospital Nacional Hipólito Unanue, a reference hospital in Lima (Peru), were used. Serum creatinine was measured using the Jaffe’s method. Creatinine clearance was performed by simultaneous determinations of serum creatinine and urinary creatinine, obtained through 24-hour urine collection. Correlations were calculated using Pearson coefficient, considering significant values of p<0.05.Results: 426 patients were included. The average age was 58.36 +/-16.21 years, with a minimum age of 15 and a maximum of 91. There was a slight female predominance (51.2%). The correlation between creatinine clearance and that estimated by the MDRD equation was 0.57 (p<0.001); when restricting the analysis to those patients with clearance values lower than 60 ml/min, the correlation was 0.55 (p <0.001). The correlation between creatinine clearance and that estimated by the Cockcroft-Gault equation was 0.53 (p<0.001); when the analysis was limited to patients with purification values lower than 60 ml/min, the correlation was 0.55 (p <0.001). The correlation between Cockcroft-Gault and MDRD equations was 0.84 (p<0.01). In patients with purifications below 60, it was 0.87 (p<0.01). The results showed no differences when restricting observations to patients under 70. Conclusion: Although Cockcroft-Gault and MDRD equations keep a good correlation between them, this correlation is suboptimal with creatinine clearance performed through 24-hour collection, under usual clinical conditions.