BACKGROUND: malnutrition is an important risk factor for poor outcome in patients recovering after hip fracture surgery. This study aimed to investigate the clinical, nutritional and rehabilitation effects of an oral nutritional supplementation (ONS) in an inpatient rehabilitation setting. METHODS: this was an observer-blinded randomised controlled trial of elderly post-surgical proximal femoral fracture patients. A ready-to-use oral liquid nutritional supplementation (18-24 g protein and 500 kcal per day) in addition to hospital diet was compared with hospital diet only. Both groups received usual rehabilitation therapy and oral calcium and vitamin D supplements. Outcomes were compared at discharge from rehabilitation and after 4 weeks of discharge. The primary outcome parameters were the serum albumin level, the body mass index (BMI), the functional independence measure (FIM) and the elderly mobility scale (EMS). Secondary outcome parameters were frequency of complications, inpatient length of stay, mortality and acute hospital use within 6 months after discharge. RESULTS: a total of 126 patients were recruited, 65 in the supplementation arm and 61 in the control arm. There was a significant difference in change in BMI with a decrease of 0.25 and 0.03 kg/m(2) in the ONS group and 0.72 and 0.49 kg/m(2) in the control group at hospital discharge and follow-up, respectively (P = 0.012). The length of stay in rehabilitation ward was shortened by 3.80 (SE = 1.81, P = 0.04) days favouring the ONS group. The total number of infection episodes was also reduced significantly. No difference was observed in the rate of change of the serum albumin level, the FIM and the EMS. CONCLUSION: clinical and nutritional benefits were seen in this trial but rehabilitation benefits could not be demonstrated.