Background: Accurate identification and management of malnutrition is essential so that patient outcomes can be improved and resources used efficaciously. Objectives: In malnourished older adults admitted to rehabilitation: 1) report the prevalence, health and aged care use, and mortality of malnourished older adults; 2) determine and compare the criterion (concurrent and predictive) validity of the Scored Patient-Generated Subjective Global Assessment (PG-SGA) and the Mini Nutritional Assessment (MNA) in diagnosing malnutrition; and 3) identify the Scored PG-SGA score cut-off value associated with malnutrition. Design: Observational, prospective cohort. Participants/setting: Participants were 57 older adults (65 years and older; mean±standard deviation age=79.1±7.3 years) from two rural rehabilitation units in New South Wales, Australia. Measurements/statistical analysis: Scored PG-SGA; MNA; and the International Statistical Classification of Diseases and Health Related Problems, 10th revision, Australian Modification (ICD-10-AM) classification of malnutrition were compared to establish concurrent validity and report malnutrition prevalence. Length of stay, discharge location, rehospitalization, admission to a residential aged care facility, and mortality were measured to report health-related outcomes and to establish predictive validity. Results: Malnutrition prevalence varied according to assessment tool (ICD-10-AM: 46%; Scored PG-SGA: 53%; MNA: 28%). Using the ICD-10-AM as the reference standard, the Scored PG-SGA ratings (sensitivity 100%, specificity 87%) and score (sensitivity 92%, specificity 84%, ROC AUC [receiver operating characteristics area under the curve]=0.910±0.038) showed strong concurrent validity, and the MNA had moderate concurrent validity (sensitivity 58%, specificity 97%, receiver operating characteristics area under the curve=0.854±0.052). The Scored PG-SGA rating, Scored PG-SGA score, and MNA showed good predictive validity. Malnutrition can increase the risk of longer rehospitalization length of stay, admission to a residential aged care facility, and discharge to hospital or residential aged care facility instead of home. Conclusions: Malnutrition prevalence in the geriatric rural rehabilitation population is high, and is associated with increased health and aged care use. The Scored PG-SGA ratings and score are suitable for nutrition assessment in geriatric rehabilitation. The MNA may be suitable for nutrition assessment in geriatric rehabilitation, but care should be taken to ensure all malnourished patients are identified. Additional examination of the criterion validity of the Scored PG-SGA and MNA will lend confidence to these findings.