OBJECTIVES: Despite the high frequency of work-related musculoskeletal disorders, the relation between work conditions and ulnar nerve entrapment at the elbow has not been the object of much research. In the present study, the predictive factors for such ulnar nerve entrapment were determined in a 3-year prospective survey of upper-limb work-related musculoskeletal disorders in repetitive work. METHODS: In 1993-1994 and 3 years later, 598 workers whose jobs involved repetitive work underwent an examination by their occupational health physicians and completed a self-administered questionnaire. Predictive factors associated with the onset of ulnar nerve entrapment at the elbow were studied with bivariate and multivariate analyses. RESULTS: The annual incidence was estimated at 0.8% per person-year, on the basis of 15 new cases during the 3-year period. Holding a tool in position was the only predictive biomechanical factor [odds ratio (OR) 4.1, 95% confidence interval (95% CI) 1.4-12.0]. Obesity increased the risk of ulnar nerve entrapment at the elbow (OR 4.3, 95% CI 1.2-16.2), as did the presence of medial epicondylitis, carpal tunnel syndrome, radial tunnel syndrome, and cervicobrachial neuralgia. The associations with "holding a tool in position" and obesity were unchanged when the presence of other diagnoses was taken into account. CONCLUSIONS: Despite the limitations of the study, the results suggest that the incidence of ulnar nerve entrapment at the elbow is associated with one biomechanical risk factor (holding a tool in position, repetitively), overweight, and other upper-limb work-related musculoskeletal disorders, especially medial epicondylitis and other nerve entrapment disorders (cervicobrachial neuralgia and carpal and radial tunnel syndromes).