OBJECTIVES: The aim of this study was to assess the effect of an ergonomic intervention on pain and sickness absence caused by upper-extremity musculoskeletal disorders. METHODS: In this randomized controlled study, subjects aged 18–60 years (N=177) seeking medical advice due to upper-extremity symptoms were included if their symptoms, or the exacerbation of symptoms, had started <30 days prior to the medical consultation and imme­diate sick leave was not required. Workplace ergonomic improvements were made in the intervention group. Data on symptoms and sickness absences were gathered during one-year follow-up. RESULTS: Pain intensity, pain interference with work, leisure time, or sleep did not differ between the intervention and control group during the one-year follow-up. During the first three months of follow-up, the percentage of employees with sickness absence due to upper-extremity or other musculoskeletal disorders did not differ between the intervention (N=89) and control (N=84) group, but the total number of sickness absence days in the intervention group was about half of that in the control group (mean 6.2 versus 9.8 days for upper-extremity disorder and 6.0 versus 11.5 days for upper-extremity and other musculoskeletal disorders combined). During 4–12 months of follow-up, the percentage of employees with sickness absence due to upper-extremity disorder (10.1% versus 16.7%, P=0.20) or upper-extremity and other musculoskeletal disorders combined (20.2% versus 32.1%, P=0.07) was lower in the intervention than the control group. CONCLUSIONS: Our findings suggest that an early ergonomic intervention reduces sickness absence due to upper-extremity or other musculoskeletal disorders.