Non-alcoholic fatty liver disease (NASH) has become the most widespread liver disease in the world, mainly due to obesity and metabolic syndrome. We conducted a retrospective study, selecting the records of patients followed for obesity over a 2-year period. All patients over 18 years of age, with a BMI greater than 30kg/m2, without diabetes or hypertension were included. After eliminating patients with chronic liver disease, thrombocytopenia or elevated liver enzymes associated with other pathologies, notably muscular, drug or thyroid disease, we collected clinical and biological data. The FIB-4 score was calculated according to the formula: (age (years) × ASAT (U/L)/platelets (PLT) (109/L) × √ALAT (U/L)). We found that in 50 patients, a FIB-4 score below 1.30 was associated with a high negative predictive value, suggesting that severe fibrosis was unlikely in these cases. In the zone of uncertainty, corresponding to FIB-4 values between 1.30 and 2.67, we identified 18 cases, and which require further evaluation to accurately determine the level of fibrosis. Two cases had a positive predictive value for advanced fibrosis, underlining the need for early and specialized management. These results may help to improve clinical management by identifying patients at risk of severe fibrosis and providing them with the appropriate treatment.