The aim of the study was to measure the occurrence (prevalence and incidence) of episodes of acute low back pain (definite effect) in a wide sample of health workers assisting disabled patients. A questionnaire was used for the study both of true acute low back pain and of episodes of ingravescent low back pain controlled pharmacologically at the onset. The questionnaire identified overall acute and pharmacologically controlled episodes occurring in the previous 12 months, both in the course of work and over the whole life of the subject. Appropriately trained operators administered the questionnaire to 551 subjects; 481 valid answer cards were obtained from 372 females and 109 males working in medical, orthopaedic and geriatric departments. 75.4% of the sample had high exposure index levels for patient lifting. The prevalence of true acute low back pain was 9% in males and 11% in females referred to the previous 12 months. Taking acute true and pharmacologically controlled low back pain together the prevalences rose to 13.8% for males and 26.9% in females. Data from the reference populations showed that acute low back pain did not exceed 3% on average in the previous year. Since work seniority in the hospital wards was known, the incidences were calculated, giving 7.9% in females and 5.29% in males for acute low back pain, and 19% in females and 3.49% in males for pharmacologically controlled low back pain. Considering the number of episodes in 100 workers/year, acute low back pain alone reached prevalences of 13-14%. This therefore appears to confirm the positive ratio between episodes of low back pain and duties involving assistance to disabled patients.