BACKGROUND: A simple and clinically applicable prognostic scoring system for AIDS-related lymphoma (ARL) in the era of combination antiretroviral therapy (cART) is needed to better stratify patients' risks and to assist in the decision-making of therapeutic strategies. METHODS: We conducted a retrospective multicenter cohort study in 138 primary ARL patients over an 8-year period from 2013 to 2020. Survival curves were estimated using the Kaplan-Meier method. Univariate and multivariate Cox proportional hazard models were performed to identify the association between patient-, lymphoma-, and HIV-specific variables with progression-free survival (PFS) and overall survival (OS). The incremental prognostic value of novel inflammatory biomarkers in the International Prognostic Index (IPI) was evaluated by comparing the receiver operating characteristic (ROC) curves, the concordance index (C-index), and the integrated Brier score (IBS). RESULTS: The median age was 49.14 ± 14.20 (range 18-79) years, 81.9% were men, and the median follow-up was 44.94 (95% CI = 37.05-52.84) months. The 3-year OS and PFS were 39.4% (95% CI = 16.3-21.2) and 38.7% (95% CI = 14.5-19.7), respectively. We found that age, extranodal sites, bulky mass, CD4 T-cell counts, CD4/CD8 ratio, and hypoalbuminemia were associated with OS (all < 0.05) at both univariate and multivariate analyses. Of the new inflammatory markers, only the CD4/CD8 ratio was an independent prognostic parameter of OS and PFS. A lower CD4/CD8 ratio was strongly associated with adverse clinical factors, including older age, advanced Ann Arbor stage, more extranodal sites, elevated erythrocyte sedimentation rate, prior history of HIV, higher red cell distribution width ratio, hypoproteinemia, and emaciation. When the CD4/CD8 ratio was added to the IPI, the composite HIV-IPI score showed significantly better discrimination than IPI alone [AUC (95% CI): HIV-IPI, 0.83 (0.77-0.89) vs. IPI, 0.72 (0.70-0.85)]. The HIV-IPI model provided good predictive performance [C-index (95% CI): HIV-IPI, 0.82 (0.81-0.83) vs. IPI, 0.75 (0.73-0.77), < 0.001] and a satisfactory calibration function. CONCLUSIONS: The CD4/CD8 ratio, an inexpensive and readily available marker, is a powerful independent prognostic parameter in patients with ARL. Furthermore, when the CD4/CD8 ratio is used in combination with IPI, it increases prognostic ability. The useful prediction of expected outcomes in ARL can inform treatment decisions.