In recent years there has been a proliferation of nutrition screening tools but undernutrition remains prevalent amongst older subjects. Screening tools commonly include BMI as the widely-accepted ‘gold standard’ indicator of malnutrition. Whilst BMI may be an appropriate tool for population studies when it can be measured accurately in research conditions, the use of BMI in clinical practice may mask important weight changes and result in a failure to alert healthcare staff to a nutritional problem. The inclusion of BMI has been identified as a barrier to completing the screening process at ward level. Also, feedback from dietitians working with older subjects indicates that 72.5% of those using BMI express concerns that it is of limited use for practical reasons or that the reference range (20–25 kg/m2) is not appropriate to older subjects. Further evidence questions whether or not BMI is applicable for inclusion in methods used to identify an older subject at risk of undernutrition in a variety of care settings. In view of these findings it is advocated that weight change over a period of time together with clinical judgement is a far superior prognostic indicator of undernutrition. Despite screening, there is evidence that inpatients continue to lose weight before discharge. Further experiential evidence from both community and ward settings suggests that inadequacies in care planning, food provision and a lack of assistance with feeding are common. In order to improve the management of undernutrition in older subjects it is therefore recommended that the focus of attention should be on addressing these practical issues and on the effective monitoring of these processes.