We constructed noninvasive models to predict significant fibrosis (F ≥ 2) and advanced fibrosis (F ≥ 3) among human immunodeficiency virus (HIV)/hepatitis C virus (HCV)‐coinfected patients, naïve for anti‐HCV treatment. A total of 296 patients with liver biopsy were randomly assigned to an estimation group (EG = 226; 70%) and a validation group (VG = 70; 30%). We developed the Hospital Gregorio Marañón (HGM)‐1 index, based on platelet count, aspartate aminotransferase (AST) and glucose, to predict F ≥ 2 and the HGM‐2 index, based on platelet count, international normalized ratio, alkaline phosphatase and AST to predict F ≥ 3. The area under the receiver operating characteristic curves (AUROCs) of the HGM‐1 index for the EG and the VG were 0.807 and 0.712 respectively. The AUROCs of the HGM‐2 index for the EG and the VG were 0.844 and 0.815 respectively. With the HGM‐1 index applied to the VG, using best cutoff scores, the negative predictive value (NPV) to exclude F ≥ 2 was 54.5% and the positive predictive value (PPV) to confirm F ≥ 2 was 93.3%. With the HGM‐2 index applied to the VG, using best cutoff scores, the NPV to exclude F ≥ 3 was 92.3, and the PPV to confirm F ≥ 3 was 64.3%. Thus, HGM‐2 accurately predicted F ≥ 3 among HIV/HCV‐coinfected patients. HGM‐1 was less accurate at predicting F ≥ 2.