OBJECTIVES: To assess the influence of working conditions and individual factors on the incidence of neck and upper limb symptoms among professional computer users. METHODS: The study is a prospective cohort study with an observation period of 10 months. A baseline questionnaire about symptoms in the neck, shoulder and arm/hand during previous month, individual factors, work content, physical and psychosocial work-related exposures was answered by 1,283 computer operators (response rate 84%). Incidence data were collected by ten monthly questionnaires regarding the occurrence of symptoms categorized into three gross body regions: neck, shoulders and arms/hands. A case, in the specific gross body region, was defined as a subject who was classified as non-symptomatic in that region at baseline or during minimum one follow-up period and later reported symptoms (>or=3 days). Univariable and multivariable incidence rate ratios with 95% confidence intervals for first occurrence of neck, shoulder and arm/hand cases, respectively, were calculated with Cox regression analysis. RESULTS: The incidence rate was 67, 41 and 47 cases per 100 person years for neck, shoulder and arm/hand symptoms, respectively. In the multivariable analyses, comfort of the computer work environment and gender were related to the incidence of symptoms in all body regions (RR = 1.5-1.9 for low comfort and 1.8-2.1 for females, respectively). Duration of mouse use predicted arm/hand symptoms (RR = 1.7 for >or=3 h/day) and job strain (high demands and low decision latitude) predicted neck symptoms (RR = 1.6 and 2.2 for medium and high strain, respectively). Additionally, age was related to neck and shoulder symptoms. CONCLUSION: Preventive strategies to reduce neck and upper limb symptoms among computer users should include measures to reduce mouse use, to increase the comfort of the work environment and to reduce job strain. Although the effect estimates were relatively weak to moderate, preventive measures may have a marked impact on the incidence of neck and upper limb symptoms in the general population because of the widespread use of computers in working life as well as at home.