The aim of this study was to assess, in a prospective cohort of nurses, the risk factors associated with six back pain indicators: back pain (BP), chronic or recurring BP (occurring often or lasting for more than 3 months), cervical (CP), dorsal (DP) and lumbar (LP) pain and medical treatment for BP. In 1980, a sample of 469 nurses was randomly selected from six public sector hospitals. They were followed up and interviewed in 1980, 1985 and 1990. BP indicators were assessed on the basis of the nurses' self-reports during the 12 months before questionnaire administration in 1990. The data collected were subjected to cross-sectional analysis in 1990, to study the associations between the six BP indicators and the risk factors. In a longitudinal analysis, the 1990 BP indicators were analysed in relation to the risk factors present in 1985 among the 210 nurses who were still working in hospitals in 1990 and had not suffered from musculoskeletal disorders (MSDs) between 1980 and 1985. Of the 310 nurses still working in hospitals in 1990, 57.9% had suffered from BP within the previous 12 months, 23.6% of them from CP, 23.0% from DP and 41.1% from LP, 40.5% had suffered from chronic or recurring BP, 31.1% had undergone treatment and 7.4% had taken sick leave for BP. In 1990, BP accounted for 35.8% of the total number of days of sick leave.(ABSTRACT TRUNCATED AT 250 WORDS)