Background: Undernutrition is common in older people admitted to hospital, but little is known about how nutritional state changes after discharge. Objective: This randomised controlled trial was designed to examine the effect of oral nutritional supplementation of undernourished very old people prepared to take supplements after hospital discharge following acute illness. Methods: Participants aged ≧75 years with a BMI ≤24 kg/m<sup>2</sup> and triceps skin fold thickness or mid-arm muscle circumference below the 10th centile and/or weight loss ≧5% during an acute hospital stay were allocated at random to either oral nutritional supplementation for 8 weeks from hospital discharge or to usual care. Primary outcome was change in weight, secondary outcomes were handgrip strength and anthropometry. Results: Of 198 patients eligible to participate, 136 patients (mean age 85 years) were randomised and 76/136 (56%) completed the study. Twenty percent (13/66) of the intervention group withdrew after only 2 weeks, citing intolerance of the supplements. Using intention-to-treat analysis, body weight increased by a mean of 1.6 and 2.2% in the control and intervention groups, respectively, but this between-group difference was not significant (p = 0.188). However, handgrip strength increased more (p = 0.055) in the intervention group (13.9%) than in the control group (7.2%). Conclusions: Oral nutritional supplementation was associated with a greater increase in handgrip strength than in non-supplemented controls and this observation merits further study.