In a cross-sectional, and one year retrospective study low back pain risk was analysed in a sample of 1812 subjects stratified by five professions: nurses, industrial workers, truck drivers, construction workers and white collar workers. Data were collected by occupational physicians during annual systematic examinations. Relative risks were significantly higher in nurses and industrial worker occupations than in the control group of white collar employees. Multivariate analysis points out that heavy or light handling, bad postures, non-sitting jobs and exposure to vibration or inclemency are the prevalent occupational factors of low back pain. Housekeeping among females and gardening or odd jobs in males are less but significant extra-professional factors. Prevention should include instruction in lifting techniques and improvement in work conditions.