BACKGROUND: The association between body mass index (BMI) and kidney stone formation may vary across different age groups and follow nonlinear patterns. METHODS: This study analyzed data from NHANES 2009-2018, including 14,880 participants aged ≥20 years, to evaluate the association between BMI and the risk of kidney stones. BMI was categorized as normal weight (<
25.0 kg/m RESULTS: After adjusting for confounders, participants with a BMI ≥30 kg/m CONCLUSION: High BMI is significantly associated with an increased risk of kidney stones, particularly among middle-aged and older adults. The relationship between BMI and kidney stones is non-linear, highlighting the need to develop age-specific BMI management strategies to reduce the occurrence of kidney stones.