Objectives To determine the usefulness of the Mini Nutritional Assessment (MNA) and plasma amino acid analysis in predicting the formation of pressure ulcers (PUs) in inpatients. Design Prospective, observational cohort study with a mean observation period of 62.2 (plus or minus) 86.4 days. Setting Intermediate and acute care wards of a hospital in rural Japan. Participants Inpatients with an average age of 85.0 (plus or minus) 7.6 (N = 422). Measurements Mini Nutritional Assessment, Subjective Global Assessment (SGA), Braden Scale (PU prognostic score), PU formation, and biochemical analysis including plasma amino acid concentrations. Results PUs developed in 7.1% of participants. A MNA score of less than 8 was more sensitive than a rating of moderate or severe malnourishment on the SGA combined with a Braden Scale score of less than 15 in predicting future PUs. The area under the receiver operating characteristic curve (AUC) of the MNA was superior to that of the Braden Scale. The Braden Scale nutrition subscore had the lowest AUC of the six Braden Scale subscores. Individuals who developed PUs had significantly lower plasma arginine concentrations than those who did not. Conclusion Mini Nutritional Assessment was able to predict the development of PUs. A MNA score of less than 8 performed better than the SGA, Braden Scale, and plasma arginine levels in predicting PU development. Although lower plasma arginine concentration at time of admission was associated with PU development, the AUC for arginine was not significantly different from 0.50. The findings from this prospective study support the use of nutritional assessment in inpatients to predict PU risk and target appropriate interventions. (copyright) 2013, The American Geriatrics Society.