BACKGROUND: Non-alcoholic fatty liver disease (NAFLD) is an increasing public health concern in Vietnam, particularly among working-age adults (18-60 years). The rs738409 variant (C>G) is a well-established risk factor for NAFLD globally; however, its impact on the Vietnamese population remains inadequately studied. This study investigates its association with NAFLD risk and its interaction with metabolic factors. METHODS: A case-control study was conducted with 135 NAFLD patients and 270 age- and sex-matched controls, collected from April to August 2023. Hepatic steatosis was evaluated via ultrasound, and NAFLD was diagnosed in cases without excessive alcohol consumption and other liver conditions. Data on demographics, clinical characteristics, and biochemical markers (eg, lipid profiles, liver enzymes) were collected. The rs738409 variant was genotyped using real-time PCR. Statistical methods included Hardy-Weinberg equilibrium testing, allele and genotype frequency comparisons, multivariable logistic regression adjusting for metabolic covariates, and ROC curve analysis to evaluate the predictive accuracy of rs738409. RESULTS: The frequency of the G allele was significantly higher in NAFLD patients (35.93%) compared to controls (28.15%, = 0.024). Individuals with CG+GG genotypes exhibited an increased risk of NAFLD (OR = 1.433, = 0.042), with a stronger association in those with low HDL-c (OR = 2.074, = 0.009). However, multivariable logistic regression analysis indicated that the rs738409 variant was not an independent risk factor for NAFLD in this population, in contrast to obesity and high triglycerides. ROC analysis revealed rs738409 alone had limited predictive power for NAFLD (AUC = 0.5537) but predictive accuracy improved slightly when combined with metabolic factors such as BMI and triglyceride levels (AUC = 0.7840). CONCLUSION: The rs738409 variant modestly increases NAFLD risk in Vietnamese working-age adults, particularly in those with dyslipidemia. However, metabolic factors, such as obesity and lipid disorders, play a more dominant role. This underscores the importance of lifestyle interventions and metabolic control in NAFLD management.