Protein–energy malnutrition and nosocomial infection (NI) are frequent in elderly patients, and a causal link between the two has often been suggested. The aim of the present study was to identify the nutritional parameters predictive of NI in elderly patients. We assessed on admission 101 patients (sixty-six women, thirty-five men, aged over 65 years) admitted to an acute care of the elderly department. Sarcopenia was detected by dual-energy X-ray absorptiometry, with appendicular skeletal muscle mass expressed with respect to body area. Weight, BMI, albuminaemia, serum transthyretin and C-reactive protein values were also determined on admission, and known risk factors, such as functional dependence and invasive biomedical material, were also evaluated. After up to 3 weeks of hospitalisation, patients were classified according to whether they had developed an NI. After 3 weeks of hospitalisation, we found that twenty-nine patients had suffered an NI, occurring after a mean of 16·1 d. Patients who were sarcopenic on admission had a significantly higher risk of contracting an NI (relative risk 2·1, 95 % CI 1·1, 3·8). None of the other morphometric or biological parameters differed significantly between the two groups of patients on admission. Patients who experienced an NI were also more likely, on admission, to have a medical device (P=0·02 to P=0·001 depending on the device), to have swallowing problems (P=0·002) or to have restricted autonomy (P<0·01). Sarcopenia on admission to an acute care of the elderly unit, as measured by X-ray absorptiometry, was therefore associated with a doubled risk of NI during the first 3 weeks of hospitalisation.