Introduction: The goal of this study was to assess the effectiveness of a group-based interactive work style intervention in improving work style behavior. Methods: Computer workers with neck and upper limb symptoms were randomised into the work style group (WS, N = 152), the work style and physical activity group (WSPA, N = 156), or the usual care group (N = 158). Both intervention groups received the same work style intervention but the WSPA group also received a lifestyle physical activity intervention. Participants from the intervention groups attended six group meetings which focused on behavioral change with regard to body posture and workstation adjustment, breaks, and coping with high work demands in order to reduce work stress. Stage of change, breaks and exercise behavior, and stress outcomes were assessed by questionnaire at baseline (T0) and after 6 (T1) and 12 months (T2). Body posture and workstation adjustment were assessed by observation and by questionnaire at T0, T1, and T2. Multilevel analyses were used to study differences in work style behavior between study groups. Results: The work style intervention was effective in improving stage of change with regard to body posture, workstation adjustment, and the use of sufficient breaks during computer work. These findings were confirmed by higher self-reported use of breaks and exercise reminder software and less working hours without breaks. However, self-reported changes in body posture and workstation adjustment were less consistent. The work style intervention was ineffective in changing stress outcomes. Conclusion: A group-based work style intervention seems to be effective in improving some elements of work style behavior. Future studies should investigate the effectiveness of work style interventions on all dimensions of the Feuerstein work style model. © 2007 Springer Science+Business Media, LLC.