BACKGROUND: Various nutritional assessment tools are available to assess adult undernutrition, but few are practical in poorly served areas of low-income countries. OBJECTIVE: The objective was to assess the relation between midupper arm circumference (MUAC), weight, body mass index (BMI), and clinical assessment for edema in predicting mortality in adults with severe acute undernutrition. DESIGN: Demographic and anthropometric data that were collected in an observational study of 197 adults were analyzed. Participants were aged 18-59 y and were admitted to a therapeutic feeding center in Ajiep, Southern Sudan, during the height of the 1998 famine. Receiver operating curves were calculated and compared. RESULTS: The mean (±SD) age of the participants was 40.1 ±10.8 y, and the mean (±SD) MUAC, weight, and BMI (in kg/m(2)) were 16.4 ± 1.3 cm, 35.1 ± 5.2 kg, and 12.6 ± 1.5, respectively. The area under the receiver operating curve for MUAC (0.71) was higher (P = 0.01) than those of BMI (0.57) and weight (0.51). Mean age, weight, and BMI on admission did not differ between survivors and nonsurvivors (P > 0.17). MUAC and edema were independently associated with mortality. For every 1-cm increase in admission MUAC, the odds of subsequent mortality decreased by 58% (adjusted OR: 0.42; 95% CI: 0.28, 0.63; P < 0.001). CONCLUSIONS: In this study, which was conducted at the height of a major famine among adults with extremely severe grades of undernutrition, MUAC and edema were better indicators of short-term prognosis than was BMI. Further studies are needed to define a critical MUAC threshold for the diagnosis of acute adult undernutrition.