ABSTRACT INTRODUCTION For two decades, various countries have experienced an epidemic of chronic kidney disease unexplainable by traditional causes. Typically a chronic tubulointerstitial nephritis, it predominantly affects young male agricultural workers and has been reported in several countries in Central America, as well as in Sri Lanka, India and Egypt. Recent studies in El Salvador have also reported the disease in male nonagricultural workers and in women, both those working in agriculture and not. Epidemiological information on whether this condition affects pediatric populations is virtually nonexistent. Globally, estimates of chronic kidney disease prevalence in pediatric populations range from 21 to 108 per million population. OBJECTIVE Determine the prevalence of urinary markers of renal damage and of chronic kidney disease in persons aged <18 years in rural Salvadoran communities. METHODS Pediatric NefroSalva was a descriptive epidemiologic study in three agricultural regions with known high prevalence of chronic kidney disease of uncertain etiology: Bajo Lempa, Guayapa Abajo and Las Brisas. Demographic and health data were collected and physical measurements were taken for 2115 persons aged <18 years, 1058 boys and 1057 girls. Urine samples were tested for markers of renal damage and blood samples analyzed to measure creatinine for estimating glomerular filtration rate (Schwartz formula). Median glomerular filtration rate was compared with reference values for age groups 2-12 and 13-17 years; mean glomerular filtration rate trends were assessed for age groups 2-5, 6-12 and 13-17 years. Positive test results were confirmed after three months. RESULTS Prevalence of urinary markers of renal damage was 4%, 4.3% in girls and 3.8% in boys. Microalbuminura (albumin:creatinine ratio 30-300 mg/g) was detected in both sexes and all age groups in all three regions, with prevalences of 2.6%-3.8% in boys and 3.3%-3.8% in girls. Macroalbuminuria (albumin:creatinine ratio >300 mg/g) was detected only in girls in Las Brisas, 2.3%. Glomerular hyperfiltration (compared to international norms) was found in all age-sex groups in all three regions. Prevalence of chronic kidney disease was 3.9%—4.1% in girls and 3.6% in boys. The prevalence of chronic renal failure was 0.1%. CONCLUSIONS High prevalence of chronic kidney disease in children and adolescents calls attention to the need for primary prevention from very early ages. This finding in children in areas where chronic kidney disease of uncertain etiology is common in adults is consistent with a contribution of environmental toxins to the epidemic observed in these areas.