Objectives: This study aimed to evaluate the association between the platelet–albumin–bilirubin (PALBI) score and disease severity in hyperemesis gravidarum (HG), and to assess its discriminative performance for identifying severe cases. Methods: This study was a retrospective analysis of prospectively collected data conducted at a tertiary care center between January 2022 – December 2025. Pregnant women diagnosed with HG and gestational age–matched healthy controls were included. After 1:2 propensity score matching, patients were categorized into mild/moderate and severe HG based on Pregnancy-Unique Quantification of Emesis (PUQE-24) scores. Clinical and laboratory parameters were analyzed. Multivariable logistic regression was performed to evaluate independent associations. Diagnostic performance was assessed using receiver operating characteristic (ROC) analysis, and internal validation was conducted using bootstrap resampling. Results: A total of 330 participants were included (220 HG, 110 controls). The PALBI score increased significantly with disease severity (p < 0.001). In multivariable analysis, the PALBI score was independently associated with severe HG (adjusted odds ratio [aOR]: 2.32; 95% confidence interval [CI]: 1.85–2.92; p < 0.001). The PALBI score demonstrated good discriminative performance for identifying severe HG (area under the curve [AUC]: 0.814). At the optimal cut-off value (> –2.52), sensitivity and specificity were 80.9% and 75.8%, respectively. Internal validation confirmed model stability (AUC: 0.810). Adding PALBI to PUQE-24 significantly improved discrimination for prolonged hospitalization, defined as >4 days (AUC: 0.81 vs. 0.74; p = 0.035). The PALBI score also showed moderate performance in distinguishing HG from controls (AUC: 0.735). Conclusions: The PALBI score appears to be associated with disease severity in HG and shows acceptable discriminative performance for identifying severe cases. As a readily available composite biomarker, it may have potential utility in supporting risk stratification.