The estimated glomerular filtration rate (eGFR) using serum creatinine is widely utilized for assessing renal function. Its decrease with age and in the presence of chronic diseases such as diabetes, hypertension, and obesity is well-known. However, there are no representative data for the Chilean population. Aim: To estimate the decline in eGFR with age according to gender and the presence of chronic diseases in the adult Chilean population. Methods: This cross-sectional study involved 5,638 participants aged >= 18 years from the National Health Survey 2009 and 2017. The eGFR was estimated using the CKD-EPI formula based on serum creatinine. The decline in eGFR was compared by gender and the presence of chronic diseases (diabetes, hypertension, dyslipidemia, and/or obesity). Results: eGFR declined with age in both genders, with a steeper decrease in women (-0.88 vs.-0.78 mL/min/1.73 m(2)/year, p<0.01). The decline in eGFR started early and uniformly from the age of 18. In the presence of chronic diseases, the slope was significantly steeper (-0.94 vs.-0.83 mL/min/1.73 m(2)/year, p<0.001), with women with chronic diseases experiencing the greatest decline (-1.00 mL/min/1.73 m(2)/year). 2 /year). Conclusion: eGFR progressively decreased with age in the Chilean population, showing an early decline starting from 18 years, more pronounced in women, and in the presence of chronic diseases. Our findings provide relevant population-based information for interpreting eGFR across different age groups and risk categories.