Office workers remain in a awkward position for long periods, which can lead to musculoskeletal symptoms. Ergonomic guidelines are recommended to avoid such problems. Evidence of the long-term effectiveness of ergonomic interventions is scarce. The aim of this randomised controlled trial was to compare pain intensity among office workers who received an ergonomic intervention and a control group before as well as 12, 24, and 36 wk after the intervention. Workers were randomly allocated to a control group (CG) and experimental group (EG). The EG received an ergonomic workstation intervention. Furniture measurements were related to individual anthropometric measurements to identify mismatches. The outcome was pain intensity, which was determined using a numerical pain scale and the Nordic Musculoskeletal Questionnaire. A linear mixed model was created with pain intensity as the dependent variable. Group and time were the independent variables. No significant interactions were found between group and time. Significant differences between groups were found for the pain intensity in the neck, shoulder, upper back, and wrist/hand (p<0.05), with lower intensity in the EG. The intervention reduced pain intensity in the neck, shoulder, upper back, and wrist/hand. However, no reduction in pain intensity was found for the lower back or elbow.