OBJECTIVES: To investigate whether a group-based stress management intervention, based on principles from cognitive behaviour therapy, can reduce stress and alter coping strategies in an occupationally diverse population with extensive symptoms of work-related stress. METHODS: Using a randomized wait list control design, 102 participants were divided into two groups: intervention and wait list control (WLC). The intervention was a three-month group-based stress management program. Outcomes measures were the Perceived Stress Scale (PSS-10, range 0–40 points) and five dimensions from the Brief COPE questionnaire (range 2–8 points) at baseline and three-, six- and nine-months follow-up. Data were analyzed with a univariate analysis of variance. RESULTS: On the PSS-10 from baseline to three months, the intervention group changed -6.45 (95% CI -8.25–-4.64) points, compared to -1.12 (95% CI -2.94–0.70) points in the WLC group. The between-groups difference was -5.32 (95% CI -7.89–-2.76) points, equalling a standardized mean difference of -0.84 (95% CI -1.27–-0.42) favouring the intervention. One coping dimension, positive reframing, differed between the two groups. Here the intervention group changed -0.86 (95% CI -1.25–-0.48) points from baseline to three months, compared to -0.18 (-0.58–0.22) points in the WLC-group. We found a between-groups difference of -0.67 (95% CI -1.24–-0.11) points, equalling a standardized mean difference of -0.48 (95% CI -0.89–-0.07) favouring the intervention. The gains achieved during treatment were maintained when followed up three months later. CONCLUSIONS: Treatment is superior to the control condition in positively affecting perceived stress and positive reframing. When followed up, the gains achieved are maintained.