The etiology and frequency of low back pain among health care personnel have been widely studied by means of cross sectional studies. The aim of our study was to calculate low back pain incidence in a prospective cohort of nursing students. A population of 344 subjects (72 males and 272 females) was involved in this investigation. Every student was submitted to a clinical and functional examination of the spine before beginning training and was checked in two following steps by a specific questionnaire for epidemiological studies of spinal disorders in working communities. 197 subjects (57.3%)(41 males and 156 females) completed follow-up. The low back pain incidence was similar at the end of two exposure periods (12.1% and 13.1%). The cumulative incidence was 22.5% throughout the study period. The longitudinal study allowed good control of selection bias and confounding factors; more over it showed that compared to other measurements of occurrence the cumulative incidence was between other occurrence measures, more informative, in our case, than prevalence and incidence rates. A cumulative incidence of low back pain over 20% after only two years of exposure in a young and healthy population of nursing students, requires implementation of ergonomic measures for patient handling tasks.