This longitudinal, quasi-experiment tested whether a work reorganization intervention can improve stress-related outcomes by increasing people's job control. To this end, the authors used a participative action research (PAR) intervention that had the goal of reorganizing work to increase the extent to which people had discretion and choice in their work. Results indicated that the PAR intervention significantly improved people's mental health, sickness absence rates, and self-rated performance at a 1-year follow-up. Consistent with occupational health psychology theories, increase in job control served as the mechanism, or mediator, by which these improvements occurred. Discussion focuses on the need to understand the mechanisms by which work reorganization interventions affect change.