Reviewing Workers' Compensation records for back injury from a large university hospital for a 2-year period, we found a yearly incidence of lost work time back injury among nurses of 2.0% per year, exceeded only by physical plant staff, who had a rate of 3.5%. Nurses' aides had an injury rate 3.3-fold higher than registered nurses and licensed practical nurses and higher than any other occupational group. We compared 100 cases of nurses with back injury in the previous 2 years with 197 noninjured control subjects using a mailed 40-item questionnaire. Multivariate logistic modelling showed that prior nonback injury and performing combined lifting activities were statistically significant risk factors for back injury, and being overweight approached significance, after adjusting for the effects of age, gender, and each of the evaluated risk factors.