Objectives: To evaluate whether protein and energy supplementation influences recovery after hip fracture. Design: Systematic review of randomised and quasi-randomised trials in people aged 65 y and over. Data sources: We searched seven electronic databases from 1966 to April 2002, four journals and reference lists of relevant articles. We contacted trial investigators and experts for details of other trials. Main outcome measures: Mortality, complications and unfavourable outcome (mortality or survivors with complications) were the primary outcomes. We also sought data on length of hospital stay, functional status after hip fracture, quality of life and compliance with supplementation. Results: In total, 12 randomised trials involving 898 participants were included. Nine trials evaluated protein and energy supplementation (five oral and four nasogastric feeding), and a further three trials tested oral protein supplementation. Potential biases resulting from inadequate allocation concealment and lack of assessor blinding and intention-to-treat analysis, as well as the limited outcome data, mean that the results must be interpreted with caution. Pooled data from eight of the nine trials evaluating protein and energy supplements showed no evidence for an effect on mortality (relative risk 0.92, 95% CI 0.56-1.50). Limited data from only three trials showed that oral protein and energy supplements may reduce unfavourable outcome (relative risk 0.52, 95% CI 0.32-0.84). Conclusion: Based on limited evidence, oral protein and energy supplementation after hip fracture may reduce unfavourable outcome. Further evidence from good-quality randomised trials is required to inform clinical practice.