Prediksi mortalitas bersifat esensial pada manajemen perawatan intensif. Acute Physiologic and Chronic Health Evaluation II merupakan sistem skor kompleks yang umum digunakan di Intensive Care Unit (ICU), sedangkan osmolalitas plasma merupakan salah satu sistem skor parameter tunggal yang diketahui dapat menjadi alternatif prediktor mortalitas di ICU. Tujuan penelitian untuk mengetahui besar nilai area undercurve (AUC), sensitivitas, spesifisitas, nilai prediksi positif, nilai prediksi negatif dari kedua prediktor dan mengetahui adanya perbedaan bermakna dari nilai AUC kedua prediktor tersebut. Penelitian merupakan uji diagnostik metode cross sectional yang melibatkan 134 subjek. Uji diagnostik menggunakan kurva ROC dan tabel 2x2. Perhitungan data didapatkan nilai AUC osmolalitas plasma sebesar 75,9% (IK95% 67,7 sampai 84,3%), dengan cut off point 297 mOsm/kg, sensitifitas 70,0%, spesifisitas 79,7%. Tabel 2x2 menghasilkan NDP sebesar 79,0% (IK95% 66,8 sampai 88,3%), NDN 70,8% (IK95% 58,9 sampai 81%). Nilai AUC APACHE II sebesar 83,4% (IK95% 76,5 sampai 90,3%) dengan cut off point sebesar 24, sensitifitas 72,9%, spesifisitas 81,3%. Tabel 2x2 menghasilkan NDP 81,0% (IK95% 69,1 sampai 89,8%), NDN 73,2% (IK95% 61,4 sampai 83,1%). Analisis ROC didapatkan nilai P=0,19. Nilai AUC osmolalitas plasma tergolong level sedang (>70-80%), APACHE II tergolong level baik (>80-90%). Analisis ROC dengan P>0,05 menyatakan tidak terdapat perbedaan bermakna antara kurva ROC kedua prediktor. Sekalipun osmolalitas plasma memiliki nilai diagnostik sedang, dibandingkan APACHE II dengan nilai diagnostik baik tetapi perbedaan nilai tersebut tidak bermakna sehingga osmolalitas plasma dapat digunakan sebagai alternatif APACHE II untuk prediktor mortalitas di ICU. Prediction of in-hospital mortality is essential for management of intensive care. Complex scoring system commonly used is APACHE II, meanwhile plasma osmolality is a single parameter scoring system that has known to be an alternative for mortality predictors in the Intensive Care Unit (ICU). The objective of this study was to determine the area undercurve (AUC) value, sensitivity, specificity, positive predictive value, negative predictive value for both predictors and to determine significant differences in AUC values in both scoring system. This was a diagnostic test with cross-sectional method that included 134 subjects. Diagnostic test using ROC curves and 2x2 tables. Result of plasma osmolality with AUC 75.9% (95%CI 67.7 to 84.3%). Cut off point was 297 mOsm/kg, sensitivity was 70.0%, and specificity was 79.7%. Two point two table with PPV 79.0% (95%CI 66.8 to 88.3%) and NPV 70.8% (95%CI 58.9 to 81%). The AUC for APACHE II was 83.4% (95%CI: 76.5 to 90.3%). Cut off point was 24, sensitivity was 72.9%, and specificity was 81.3%. Two point two table with PPV 81.0% (95%CI 69.1 to 89.8%) and NPV 73.2% (95%CI 61.4 to 83.1%). ROC analysis with P value=0.19. AUC values of plasma osmolality was at moderate level (>70 to 80%), APACHE II at good level (>80 to 90%). ROC analysis with P>0.05 states there was no significant difference between the ROC curves in both predictors. Although plasma osmolality has moderate diagnostic value, compared with APACHE II, with a good diagnostic value but the value differences was unsignificant thus plasma osmolality can be used as an alternative of APACHE II for mortality predictors in critically ill patients in the ICU.