Weight index (WI), triceps skinfold (TSF), serum albumin and delayed cutaneous hypersensitivity reaction (DCH) were measured in 96 hospitalized elderly patients and in 100 age- and sex-matched free-living controls. Using the 10th percentile of data obtained in the controls, WI was subnormal in 35 % of the patients. Corresponding findings with regard to TSF, serum albumin and DCH were 32, 50 and 31%, respectively. The findings in the controls were mainly within the range observed in national reference groups. Patients were considered malnourished if they showed at least two variables (of which one was required to be anthropometric) below the cut-off limits used. When these limits were set at the 10th percentile of the recordings in the controls, the occurrence of undernutrition in the patients was 39%. By using the 5th percentile the corresponding figure was 16%. Malnourishment was most pronounced in patients with multiple organ disease and malignancy. It is concluded that low nutritional indices are a common occurrence in elderly subjects admitted to hospital and that undernutrition is related to the nature of the disease rather than age.