Prevalence of malnutrition, particularly undernutrition, increases with advancing age, and patients with hip fracture are often particularly malnourished and/or undernourished. Deficiency in both micronutrients and macronutrients appears to be strongly implicated in the pathogenesis and the consequences of hip fracture in osteoporotic elderly. Such deficiencies can accelerate age-dependent bone loss, increase the propensity to fall by impairing movement coordination, and affect protective mechanisms that reduce the impact of falling. With respect to micronutrients, the most documented information concerns calcium and vitamin D. Studies conducted in the elderly have shown that administration of calcium and vitamin D can reduce femoral bone loss and, in institutionalized patients, lower the incidence of hip fracture. Besides hypovitaminosis D, deficiency in vitamin K has been suggested to contribute to bone fragility in patients sustaining hip fracture. As far as macronutrients are concerned, low protein intake appears to play a distinct detrimental role in the causes and complications of hip fracture. In a recent survey in hospitalized elderly patients, reduced protein intake was associated with lower femoral neck bone mineral density (BMD) and poor physical performance. This observation is in keeping with several studies in which a state of energy-protein malnutrition was documented in elderly patients with hip fracture. In these patients, in whom we detected very low femoral neck bone mineral density at the level of the proximal femur, the self-selected intake of protein and energy was insufficient during their hospital stay. Interestingly, the clinical outcome after hip fracture was significantly improved by daily oral nutritional supplement normalizing the protein intake, documented as a reduction in both complication rate and median duration of hospital stay. Further studies showed that normalization of the protein intake, independently of that of energy, calcium, and vitamin D, was responsible for this more favorable outcome. Preliminary data suggest that protein supplementation may also reduce further bone loss in elderly patients having sustained hip fracture. Increasing the protein intake from low to normal could act through an increase in the plasma level of IGF-I, a growth factor that exerts a positive effect on bone mass and that has been found to decrease with aging.