In France, although there are 445,000 beds in nursing homes (NHs) for elderly people, no studies on the burden of infections in NHs have been published. We sought to estimate the prevalence of infection among the residents and to assess the extent to which infections were associated with the residents' risk factors. We performed a nationwide, multicentre, cross-sectional, clustered period prevalence survey over five one-month periods. Cases of infection were classified as definite or, in the absence of laboratory confirmation, as probable. A total of 44,869 residents in 578 volunteer facilities were enrolled in the survey. The overall prevalence rate of infections was 11.23% [95% confidence interval (CI): 10.50-11.97] and differed significantly (P<0.001) across survey periods (the time of the year the survey was carried out). The rate of definite cases was 4.60% (95% CI: 4.04-5.54) and the rate of probable cases was 6.63% (95% CI: 5.77-7.98). Respiratory tract infections were the most frequent and accounted for 41% of all infections. Infections were significantly associated with age, length of stay, full disability, urinary device, bedsores and the survey period. Only prevention programmes may reduce the impact of infections on this frail population.